#include<stdio.h>
int main(){
    int num, top=-1,size=5;
    int arr[25];
    scanf("%d",&num);
    int isFull(){
        if(top==size-1){
        return 1;
       }
       else{
           return 0;
       }
    }
    void push(int num){
    if(isFull()){
        printf("stack is full\n");
    }
    else{
        arr[++top];
    }
    
  }
  int isEmpty(){
        if(top==-1){
         return 1;
            }
        else{
            return 0;
        }
    }
    void pop(){
    if(isEmpty()){
        printf("stack is empty\n");
    }
    else{
        top--;
    }
}
void traverse{
    for(int i=0;i<=top;i++){
        scanf("%d",&size);
        push(num);
    }
  if(num<0){
    printf("Invalid input");
    }
}
pop();
traverse();
return 0;
}