#include<iostream>
#include<stack>
#include<queue>
#include<string>

using namespace std;

stack <int> s;
string a;
int x;

int main(){
    while(1){
        cin>>a;
        if( a == "push"){
            cin>>x;
            s.push(x);
        }
        else if ( a == "pop"){
            s.pop();
        }
        else if( a == "top"){
            if(!s.empty()) cout<<s.top()<<endl;
            else cout<<"-1";
        }
        else if( a == "size"){
            cout<<s.size()<<endl;
        }
        else if( a == "empty"){
            if(!s.empty()) cout<<"0"<<endl;
            else cout<<"1"<<endl;
        }
        else if( a == "end"){
            break;
        }
        else if( a == "init"){
            for(int i=s.size();i>=0;i--)
                s.pop();
        }
    }
    return 0;
}