#include <stdio.h>
/* 函数功能：用迭代法计算n! */
long fact(int n)
{            /* 定义 */
    int  i;
    long result = 1;
    for (i = 2; i <= n; i++) 
    {
        result = result * i;
    }
    return result;
}
int main(void) 
{
    int  m;
    long ret;
    printf("Input m:");
    scanf("%d", &m);
    ret=fact(m);
    printf("%d! = %ld\n", m, ret);
    return 0;
}