#include<stdio.h>
#include<string.h>






int main(){
    int size;
    scanf("%d",&size);
    if(size<=0){
        printf("Invalid input");
        
    }
    if(strcmp(str,"PUSH")){
        int x;
        scanf("%d",&x);
        push(x);
    }
    else if(strcmp(str,"POP")){
        pop(x);
        
    }
    else if(strcmp(str,"PEEK")){
        peek();
    }
    else{
        display();
    }
}