#include <iostream>
using namespace std;
#define MaxSize 100000
class zhan{
private:
int a[MaxSize];
int t=0;
public:
void push(int x){
a[t]=x;
t++;
}
void pop(){
if(t>0){
t--;
cout<<a[t]<<endl;
}
else{
cout<<"error"<<endl;
}
}
void top(){
if(t>0){
cout<<a[t-1]<<endl;
}
else{
cout<<"error"<<endl;
}
}
};
int main() {
int n,x;
string ch;
zhan zh1;
cin>>n;
while(n--){
cin>>ch;
if(ch=="push"){
cin>>x;
zh1.push(x);
}
else if(ch=="pop"){
zh1.pop();
}
else zh1.top();
}
}