SDUT OnlineJudge
#include<bits/stdc++.h>
using namespace std;
int main()
{
vector<int>a;char t[100];int flag01=1;int num=-1;int key=0;int flag02=1;
while(flag01!=EOF)
{
if(num==-1 || num==key)
{
flag01=scanf("%d",&num);a.clear();key=0;
if(!flag02)
{
printf("\n");
}
flag02=0;
}
else
{
flag01=scanf("%s",t);
if(t[0]=='p' && t[1]=='u')
{
char re[100];scanf("%s",re);
a.push_back(atoi(re));key++;
}
if(t[0]=='p' && t[1]=='o')
{
key++;
if(a.empty()) printf("error\n");
else
{
a.pop_back();
}
}
if(t[0]=='t')
{
key++;
if(a.empty())printf("empty\n");
else printf("%d\n",*(a.end()-1));
}
}
}
return 0;
}