using System;

public class Program

{

    public static void Main()

    {

        int num1 = int.Parse(Console.ReadLine());

        int num2 = int.Parse(Console.ReadLine());

        bool allDigitsAreEqual = true;

        for (int i=1; i<=5 ; i++)

        {

            if(num1 % 10 != num2 % 10)

            {allDigitsAreEqual = false;

             Console.Write(num1%10);

             Console.Write(num2%10);

             return;}

            else 

            {num1 = num1 / 10;

             num2 = num2 / 10;

            }

        }

        if (allDigitsAreEqual == true)

                Console.Write("yes");

    }

}