qiushu

import java.util.Scanner;
public class JeChen {
 public static void main(String[] args) {
 Scanner in = new Scanner(System.in);
System.out.print("请输入一个整数:");
int n=input.nextInt();
System.out.println(n+"!="+f(n));
 }
 static long f(int n){
 if (n==1) 
return 1;
 else 
return n*f(n-1);
 }
}