#include <stdio.h>

int main(int argc, char** argv)
{
	int n;
	int m=1;
	scanf("%d", &n);
	goto CHK;
CHK:
	if(n < 0)
		goto ERR;
	if(n == 0)
		goto RET;	
	goto FAC;
FAC:
	m*=n;
	n = n-1;
	if(n > 0)
		goto FAC;
	goto RET;
RET:
	printf("%d\n", m);
	return 0;
ERR:
	printf("error\n");
	return -1;
}