#include <stdio.h>

int main(int argc, char** argv)
{
	int n;
	int stackPoint = 0;
	int stackTable[10];
	int ret = 1;

	scanf("%d", &n);
	goto CHK;
CHK:
	if(n < 0)
		goto ERR;
	if(n == 0)
		goto RET;	
	goto FAC;
FAC:
	stackTable[stackPoint++] = n;
	n--;
	if(n > 0)
		goto FAC;
	goto STACK;
STACK:
	ret *= stackTable[--stackPoint];
	if(stackPoint-1 < 0)
		goto RET;
	goto STACK;
RET:
	printf("%d\n", ret);
	return 0;
ERR:
	printf("error\n");
	return -1;
}