简单的循环。因为给的输入范围在之内，所以并不需要用到复杂的算法。

#include <bits/stdc++.h>

int main() {
    int n;
    while (std::cin >> n){
        long product = 1;
        for(int i=2;i<=n;i++){
            product*=i;
        }
        std::cout << product << std::endl;
    }
    return 0;
}

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNextInt()) {
            int n = in.nextInt();
            long product = 1;
            for (int i = 1; i <= n; i++) {
                product *= i;
            }
            System.out.println(product);
        }
    }
}