#include<iostream>
#include<string>
#include<iostream>
#include<cstdlib>
#include<array>
#include<cctype>
#include <fstream>
#include<cstdio>
#include< ctype.h >
using namespace std;
long long digui(int a)
{
long long d = 1;
if (a == 0)
d = 1;
else if (a > 0)
for (long long s = 1;s <= a;s++)
{
d *= s;
}
return d;
}
int main()
{
int a;
for (;;)
{
cout << "请输入:______\b\b\b\b\b\b"<<endl;
cin >> a;
cout << a << "的阶乘为:" << digui(a) << endl;
}
return 0;
}