#include<iostream>
#include<cstring>
using namespace std;
int s[100005];
char str[11];
int top =0;
void push(int x){
s[++top]=x;
}
void pop()
{ if (top > 0)
top--;
}
int query()

{if (top > 0)return s[top];
}
const char* empty()
{static char ans[10];
if(top==0)
{
strcpy(ans,"YES");

}
else{
    strcpy(ans,"NO");
}
return ans;
}
int main()
{
    int times;
scanf("%d",&times);
for (int i=1;i<=times;i++)
{
    scanf("%s",str);
if (strcmp(str, "push") == 0) {
    int x;
    scanf("%d", &x);
    push(x);
} else if (strcmp(str, "pop") == 0) {
    pop();
} else if (strcmp(str, "empty") == 0) {
    printf("%s\n", empty());
} else if (strcmp(str, "query") == 0) {
    int result = query();
    if (result == -1) {
        printf("Stack is empty\n"); // 栈为空时输出提示
    } else {
        printf("%d\n", result); // 打印整数
    }
}

}

return 0;
}