算法训练 判定数字

import java.util.Scanner;
public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner sc=new  Scanner(System.in);
        String s=sc.nextLine();
        char ch=s.charAt(0);
        if(Character.isDigit(ch)){
            System.out.println("yes");
        }
        else
            System.out.println("no");

    }

}