#include<stdio.h>
#include<stdlib.h>

int top = -1; size = 25;
int arr[size]

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

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

void push(num){
    if(isfull()){
        printf("Stack Overflow");
    }
    else{
        arr[++top]=num;
    }
}

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

void peek(){
    if(isempty()){
        printf("Stack Underflow");
    }
    else{
        printf("%d",arr[top]);
    }
}

void traverse(){
    if(isempty()){
        printf("Stack Underflow");
    }
    else{
        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\n");
    }
}