#include <iostream>
using namespace std;
 
int main()
{
    unsigned int n;
    unsigned long long factorial = 1;
 
    cout << "输入一个整数: ";
    cin >> n;
 
    for(int i = 1; i <=n; ++i)
    {
        factorial *= i;
    }
 
    cout << n << " 的阶乘为："<< " = " << factorial;    
    return 0;
}