#include <stdio.h>
int main(int argc, char const *argv[])
{
	int n, i = 1, sum = 1;
	printf("请输入一个数：\n");
	scanf("%d", &n);
	while(i <= n)
	{
		sum = sum*i;
		i++;
	}
	printf("n! is %d\n", sum);
	return 0;
}