java计算组合数

import java.util.Scanner;

public class Zuheshu {

//计算m阶乘
    public static int Fun(int m){
     int sum=0;
     if( m < 0 )
   System.out.println("input error,please input integer(bigger than 1):");
  else if( m == 1 || m == 0 )
  return 1;
  else
   sum = m * Fun(m-1);
  return sum;
    }

 public static void main(String[] args) {
  // TODO Auto-generated method stub
  Scanner in = new Scanner(System.in);
  int a,b,c,d;
     System.out.println("Please input n :");
     a = in.nextInt();
     System.out.println("Please input k :");
     b = in.nextInt();
     c = Fun(a)/(Fun(b)*Fun(a-b));
     System.out.print("Cnk=" + c);
     d = Fun(a)/(Fun(b-1)*Fun(a-b+1)) + c;
     System.out.print("Cn(k-1)=" + d);
 }

}