#include <stdio.h>
#include<stdlib.h>
int top=-1, size=25;
int arr[25];
int isFull(){
    if(top==size-1){
        return 1;
        
    }
    else
        return 0;
}
int isEmpty(){
    if(top==-1)
        return 1;
    else
        return 0;
}
void push(int num){
    if(isFull())
        printf("stack is full");
    else
       
        arr[++top]=num;
}
void pop(){
    if(isEmpty())
        printf("stack is empty");
    else
        top--;
}
void peek(){
    if(isEmpty())
        printf("stack is empty");
    else
        printf("%d",arr[top]); 
}
void traverse(){
    for(int i=0;i<size;i++){
        printf("%d",arr[i]);
    }
}
int main() {
    int choice,num;
    while(1){
        scanf("%d",& choice);
        switch(choice){
            case 1:
                scanf("%d",&num);
                push(num);
                break;
            case 2:
                pop();
                break;
            case 3:
                peek();
                break;
            case 4:
                traverse();
                break;
            case 5:
                exit(0);
            default:
                printf("Invalid input");
        }
    }
return 0;
}