#include<stdio.h>
#include<string.h>
#define MAX 100
int top=-1;
int arr[MAX];
int isfull() {
    if(top==MAX-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 is full");
    }
    else {
        top--;
    }
}
int peek() {
    if(isempty()) {
        printf("stack is full");
    }
    else {
        return 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\n",&size);
    if(size<0) {
        printf("Invalid input");
        return 0;
    }
    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;
}