#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>
#define MAX 10
void process_stack(int n) {
int stack[MAX] = {};
int sp = 0;
for (int i = 0; i < n; i++) {
char str_buf[16];
scanf("%s", str_buf);
if (str_buf[1] == 'u') {
int val;
scanf("%i", &val);
if (sp < MAX) {
stack[sp] = val;
sp++;
} else {
printf("Stack Overflow\n");
}
} else {
if (sp > 0) {
sp--;
printf("%i\n", stack[sp]);
} else {
printf("Stack Underflow\n");
}
}
}
}
int main() {
int n;
scanf("%d", &n);
getchar(); // Consume newline after number
process_stack(n);
return 0;
}