/*
 * compute factorial using recursion
 */
#include <stdio.h>

/* compute n! */
long fac(long n) {
	if (n <= 0) {
		return 1;
	}
	else {
		return n*fac(n-1);
	}
}

/* main program */
int main(void) {
	/* use "long" here to allow for a bigger range */
	long n;
	printf("enter n to compute factorial of\n");
	if (scanf("%ld", &n) == 1) {
		printf("%ld! is %ld\n", n, fac(n));
	}
	else {
		printf("not number\n");
		return 1;
	}
	return 0;
}