#include<iostream> #include<cstdio> #include<stack> using namespace std; int main(){ stack<int> Stack; int n; char op; int number; while(scanf("%d",&n)!=EOF){ for(int i=0;i<n;++i){ scanf("%c",&op); if(op=='P'){ scanf("%d",&number); Stack.push(number); } else if(op=='O'&&!Stack.empty()){ Stack.pop(); } else if(op=='A'){ if(!Stack.empty()){ printf("%d\n",Stack.top()); } else{ cout<<'E'<<endl; } } } } return 0; }