#include<stdio.h>
#include<stdlib.h>

#define MAX_SIZE 100

int main() {
    int n;
    if (scanf("%d", &n) != 1) return 0;
    
    if (n < 0) {
        printf("Invalid input");
        return 0;
    }
    
    int stack[MAX_SIZE];
    int top = -1;
    
    for (int i = 0; i < n; i++) {
        char cmd[10];
        scanf("%s", cmd);
        
        if (strcmp(cmd, "PUSH") == 0) {
            int x;
            scanf("%d", &x);
            if (top < MAX_SIZE - 1) {
                stack[++top] =x;
            }
        }
        else if (strcmp(cmd, "POP") == 0) {
            if (top == -1) {
                printf("stacks Underflow\n");
            }
            else {
                top--;
            }
        }
        else if (strcmp(cmd, "PEEK") == 0) {
            if (top == -1) {
                printf("stack Underflow\n");
            }
            else {
                printf("%d\n", stack[top]);
            }
        }
        else if (strcmp(cmd, "DISPLAY") == 0) {
            if (top == -1) {
        }
        else{
            for (int j = 0; j <= top; j++) {
                printf("%d ", stack[j]);
            }
            printf("\n");
        }
    }
}
return 0;
}