/***********************************************************
write by tjm 
用來展示recursive method
***********************************************************/
import java.io.*;
public class demo22{  
	public static void main(String args[]) throws Exception
	{  //程式進入點
		String getbr;
		BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
		int x;
		/*****請使用者輸入選項**********/
		x=5;
		while (x>=0)
		{
		  System.out.print("請輸入要計算階乘的數字：");
		  getbr = br.readLine();
		  x=Integer.parseInt(getbr);
		  if (x<0) 
		  {
		        System.out.println("謝謝！再見！");
			continue;
		  }
		  System.out.println(x+ "!="+fraction(x));
                } //while結束
	} //main 結束
	private static int fraction(int y)
	{ int ans;
		ans=1;
		if (y<=1) ans=1;
		else ans=y*fraction(y-1);
		return(ans);
	} // fraction 結束
}