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");

}

}