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

struct pile{
	char val;
	struct pile *suite;
};
typedef struct pile pile;

int empty(pile* p){
	return p==NULL;
}

void push(pile **p, char v){
	pile *new=malloc(sizeof(pile));
	new->val=v;
	new->suite=*p;
	*p=new;
}

char pop(pile **p){
	char v=(*p)->val;
	pile *temp=*p;
	*p=(*p)->suite;
	free(temp);
	return v;
}

void clear(pile **p){
	while(!empty(*p)){
		pop(p);
	}
}

char top(pile **p){
	return (*p)->val;
}