Problem:
Score : 100 points

Problem Statement

Determine if we can choose K different integers between 1 and N (inclusive) so that no two of them differ by 1.

Constraints

1\leq N,K\leq 100

N and K are integers.

Input

Input is given from Standard Input in the following format:

N K

Output

If we can choose K integers as above, print YES; otherwise, print NO.

Sample Input 1

3 2

Sample Output 1

YES

We can choose 1 and 3.

Sample Input 2

5 5

Sample Output 2

NO

Sample Input 3

31 10

Sample Output 3

YES

Sample Input 4

10 90

Sample Output 4

NO

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApp1
{
	class Program
	{
		static void Main(string[] args)
		{
			var input = Console.ReadLine().Split(' ')
				.Select(x => int.Parse(x))
				.ToArray();
			if (input[1] < 0 )
			{
				Console.WriteLine("NO");
			}
			else if (input[1] == 0 || input[1] == 1)
			{
				Console.WriteLine("YES");
			}
			else if((input[0]+1/2) >= input[1])
			{
				Console.WriteLine("YES");
			}
			else
			{
				Console.WriteLine("NO");
			}
		}
	}
}