用递归方法求 n!

#include <iostream>

using namespace std;
#define LL long long

LL fac(int n)
{
    LL f;
    if(n == 0 || n == 1)
        f = 1;
    else f = n * fac(n - 1);
    return f;
}

int main()
{
    LL n;
    while(cin >> n)
    {
        cout << fac(n) << endl;
    }
    return 0;
}