Hello, here is my code
using System;

public class Program
{
    public static void Main(String[] args)
    {

        var a = Convert.ToInt32(Console.ReadLine());
        var b = Convert.ToInt32(Console.ReadLine());

        var ans = (b-a + 1) / 2;

        if (b % 2 > 0)
            ans++;

        Console.WriteLine(ans);
    }
}

I can not find out the problem :(