#include<iostream> using namespace std; int main(){ int n; cin>>n; int h[n+1],hh=n,tt=n; for(int i=0;i<n;i++){ string str; cin>>str; if(str=="push"){ int t; cin>>t; h[hh]=t; hh--; } if(str=="pop"){ if(tt!=hh){ cout<<h[hh+1]<<endl; hh++; } else cout<<"error"<<endl; } if(str=="top"){ if(tt!=hh) cout<<h[hh+1]<<endl; else cout<<"error"<<endl; } } }