阶乘

import java.util.Scanner;
public class Digui {

 /**
  * @param args
  */
 public static void main(String[] args) {
  // TODO Auto-generated method stub
  Scanner scanner=new Scanner(System.in);
  int i=scanner.nextInt();
  if(i<=0)
  {
   System.out.println("必须输入大雨零的数字");
  }
  else
  {
   System.out.println(i+"!="+fac(i));
  }
 }
  
 public static int fac(int n)
 {
  if(n==1)
   return 1;
  else
   return n*fac(n-1);
 }
}