#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int top=-1,size=5;
int arr[25];
int isfull(){
    if(top==size-1){
        return 1;
    }
    else{
        return 0;
    }
}
void push(int num){
    if(isfull()){
        printf("stack is full");
    }
    else{
        arr[++top]=num;
    }
}
int isempty(){
    if(top==-1){
        return 1;
    }
    else{
        return 0;
    }
}
void pop(){
    if(isempty()){
        printf("Stack Underflow");
    }
    else{
        top--;
    }
}
void peek(){
    if(isempty()){
        printf("stack is full");
    }
    else{
        arr[top];
    }
    
}
void display(){
    for(int i=0;i<=top;i++){
        printf("%d",arr[i]);
    }
    printf("\n");
}
int main(){
    int size,i,num;
    char choice[20];
    scanf("%d",&size);
    for(i=0;i<=size;i++){
        scanf("%s",&choice);
        if(strcmp(choice,"push")==0){
            scanf("%d",&num);
            push(num);
        }
        else if(strcmp(choice,"POP")==0){
            pop();
        }
        else if(strcmp(choice,"PEEK")==0)){
            printf("%d",peek());
        }
        else if(strcmp(choice ,"DISPLAY")==0){
            display();
        }
    return 0;

}