1
      
       #include<iostream>


      
         2
      
       #include<stack>


      
         3
      
      
        using
      
      
        namespace
      
      
         std;


      
      
         4
      
      
        class
      
      
         min_stack


      
      
         5
      
      
        {


      
      
         6
      
      
        public
      
      
        :


      
      
         7
      
      
        void
      
       push(
      
        int
      
      
        );


      
      
         8
      
      
        void
      
      
          pop();


      
      
         9
      
      
        int
      
      
         min();


      
      
        10
      
      
        int
      
      
         size()


      
      
        11
      
      
            {


      
      
        12
      
      
        return
      
      
         data.size();


      
      
        13
      
      
            }


      
      
        14
      
      
        private
      
      
        :


      
      
        15
      
           stack<
      
        int
      
      >
      
         data;


      
      
        16
      
           stack<
      
        int
      
      >
      
         min_data;


      
      
        17
      
      
        };


      
      
        18
      
      
        void
      
       min_stack::push(
      
        int
      
      
         value)


      
      
        19
      
      
        {


      
      
        20
      
      
            data.push(value);


      
      
        21
      
      
        if
      
       (min_data.size()==
      
        0
      
       || min_data.top() >
      
         value)


      
      
        22
      
      
            { 


      
      
        23
      
      
                min_data.push(value);


      
      
        24
      
      
            }


      
      
        25
      
      
        else
      
      
        26
      
      
            {


      
      
        27
      
      
                min_data.push(min_data.top());


      
      
        28
      
      
            }


      
      
        29
      
      
        }


      
      
        30
      
      
        void
      
      
         min_stack::pop()


      
      
        31
      
      
        {


      
      
        32
      
      
        if
      
       (data.size()>
      
        0
      
      
        )


      
      
        33
      
      
            {


      
      
        34
      
      
                min_data.pop();


      
      
        35
      
      
                data.pop();


      
      
        36
      
      
            }


      
      
        37
      
      
        }


      
      
        38
      
      
        int
      
      
         min_stack::min()


      
      
        39
      
      
        {


      
      
        40
      
      
        return
      
      
         min_data.top();


      
      
        41
      
      
        }


      
      
        42
      
      
        43
      
      
        int
      
       main(
      
        int
      
       argc, 
      
        char
      
       **
      
        argv)


      
      
        44
      
      
        {


      
      
        45
      
      
        int
      
      
         n,m;


      
      
        46
      
      
        char
      
      
         ci;


      
      
        47
      
      
        while
      
      (cin>>
      
        n)


      
      
        48
      
      
            {


      
      
        49
      
      
                min_stack mystack;


      
      
        50
      
      
        for
      
       (
      
        int
      
       i=
      
        0
      
      ; i<n; i++
      
        )


      
      
        51
      
      
                {


      
      
        52
      
                   cin>>
      
        ci;


      
      
        53
      
      
        switch
      
      
         (ci)


      
      
        54
      
      
                    {


      
      
        55
      
      
        case
      
      
        '
      
      
        s
      
      
        '
      
      
        :


      
      
        56
      
                       cin>>
      
        m;


      
      
        57
      
      
                        mystack.push(m);


      
      
        58
      
                       cout<<mystack.min()<<
      
        endl;


      
      
        59
      
      
        break
      
      
        ;


      
      
        60
      
      
        case
      
      
        '
      
      
        o
      
      
        '
      
      
        :


      
      
        61
      
      
                        mystack.pop();


      
      
        62
      
      
        if
      
       (mystack.size()==
      
        0
      
      
        )


      
      
        63
      
      
                        {


      
      
        64
      
                           cout<<
      
        "
      
      
        NULL
      
      
        "
      
      <<
      
        endl;


      
      
        65
      
      
                        }


      
      
        66
      
      
        else
      
      
        67
      
      
                        {


      
      
        68
      
                           cout<<mystack.min()<<
      
        endl;


      
      
        69
      
      
                        }


      
      
        70
      
      
        break
      
      
        ;


      
      
        71
      
      
                    }


      
      
        72
      
      
                }   


      
      
        73
      
      
            }


      
      
        74
      
      
        return
      
      
        1
      
      
        ;


      
      
        75
      
      
        }


      
      
        76
      
      
        /*
      
      
        *************************************************************


      
      
        77
      
      
            Problem: 1522


      
      
        78
      
      
            User: xuebintian


      
      
        79
      
      
            Language: C++


      
      
        80
      
      
            Result: Accepted


      
      
        81
      
      
            Time:140 ms


      
      
        82
      
      
            Memory:1524 kb


      
      
        83
      
      
        ***************************************************************
      
      
        */