#include <stdio.h>
#include <string.h>
#define MAX 100
int stack[MAX];
int top = -1;
int  main(){
    int q;
    scanf("%d", &q);
    if(q < 0){
        printf("Invalid input");
        return 0;
    }
    for(int i = 0; i < q; i++){
        char command[20];
        scanf("%s",command);
        if(strcmp(command, "PUSH") == 0){
            int x;
            scanf("%d", &x);
            if(top <MAX-1){
                stack[++top]=x;
            }
        }
        else if(strcmp(command, "PEEK") == 0){
            if(top == -1){
                printf("Stack Underflow\n");
            }else{
                printf("%d\n",stack[top]);
            }
        }
        else if(strcmp(command, "POP") == 0){
            if(top == -1){
                printf("Stack Underflow\n");
            }
        }
        else{
            top--;
        }
        
    }
    else if (strcmp(command, "DIPLSY") == 0){
        if(top == -1){
            printf("Stack Underflow\n");
        }
        else{
            for(int j = 0; j <= top; j++){
                printf("%d ", stack[j]);
            }
            printf("\n");
        }
    }
    return 0;
    
}