注意递归函数的返回值要改成long不然在13以后会溢出

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        while(sc.hasNext()){
            int n=sc.nextInt();
            System.out.println(jieChen(n));
        }
    }
    public static long jieChen(int n){
        return n>1?n*jieChen(n-1):1;
    }
}