#include <stdio.h>
#include <stdint.h>
#include <string.h>
#define MAX 10
void process_stack(int n) {
int stack[MAX];
int top=-1;
int x;
char op[10];
for (int i=0;i<n;i++){
scanf("%s", op);
if (op[1] == 'u') {
scanf("%d", &x);
if (top < MAX-1){
top++;
stack[top] = x;
} else {printf("Stack Overflow\n");}
}
if (op[1] == 'o') {
if (top > -1) {
printf("%d\n",stack[top]);
top--;
} else {
printf("Stack Underflow\n");
}
}
}
}
int main() {
int n;
scanf("%d", &n);
getchar(); // Consume newline after number
process_stack(n);
return 0;
}