#include<stdio.h>
#include<string.h>
#define MAX 100
int stack[MAX];
int top=-1;
void push(int x){
    if(top == MAX -1)
    return;
}
void pop(){
    if(top == -1){
        printf("Stack Underflow\n");
    }
    else{
        top--;
    }
}
void peek(){
    if(top != -1){
        printf("%d\n",stack[top]);
    }
}
void display(){
    if(top==-1)
    return;
    for(int i=0;i<=top;i++){
        printf("%d ",stack[i]);
    }
    printf("\n");
}
int main(){
    int q;
    scanf("%d",&q);
    if(q<0){
        printf("Invalid input");