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

int hello(int n);
int goodbye(int n);
void f(int (*p)(int));

int main()
{
	f(hello);
	f(goodbye);
	return EXIT_SUCCESS;
}

void f(int (*p)(int))
{
	printf("%d\n", (*p)(10));
}

int hello(int n)
{
	printf("hello\n");
	return 2 * n;
}

int goodbye(int n)
{
	printf("goodbye\n");
	return 3 * n;
}