#include<stdio.h>
#include<string.h>

#define MAX_SIZE 100

int main() {
    int n;
    if (scanf("%d", &n) != 1) return 0;
    
    if (n < 0) {
        printf("Invalid input\n");
        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("Stack 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]);
             if (j != top) printf(" ");
         }
         printf("\n");
    }
    return 0;
    }