#include<stdio.h>

int top=-1,size=5;
int arr[20];

int isFull(){
    if(top==size-1)
        return 1;
    else
        return 0;
}

void push(int num){
    if(isFull())
        printf("full");
    else
        arr[++top]=num;
}

int isEmpty(){
    if(top==-1)
        return 1;
    else
        return 0;
}

void pop(){
    if(isEmpty()){
        printf("Stack Underflow");
    else
        top--; 
    }
}

int peek(){
    if(isEmpty())
        printf("Stack Underflow");
    else
        return arr[top];
}

void display(){
    int i;
    for(i=0;i<top;i++){
        printf("%d ",arr[i]);
    }
    printf("\n");
}

int main(){
    int size,i,num,choice;
    scanf("%d\n",&size);
    if(size<0){
        printf("Invalid input");
        return 0;
    }
    for(i=0;i<size;i++){
        scanf("%d ",&choice);
        switch(choice){
            case 1:
                scanf("PUSH %d",&num);
                push(num);
                break;
            case 2:
                printf("POP %d",pop());
                break;
            case 3:
                printf("PEEK %d",peek());
                break;
            case 4:
                printf("DISPLAY %d",display());
                break;
            default:
                printf("Invalid input");
        }
    }
}