1733: 堆栈的使用 答案太少，凑数的

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    while(cin >> n)
    {
        stack<int> sck;
        char ch;
        int num;
        for(int i=0; i<n; i++)
        {
            cin>>ch;
            if(ch == 'A')
            {
                if(sck.empty())
                {
                    printf("E\n");
                }else{
                    printf("%d\n", sck.top());
                }
            }else if(ch == 'P')
            {
                cin>>num;
                sck.push(num);
            }else if(ch == 'O')
            {
                if(!sck.empty())
                {
                    sck.pop();
                }
            }
        }
        printf("\n");
    }
    return 0;
}