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: Accepted)

using System;

namespace A___Anti_Adjacency
{
    class Program
    {
        static void Main (string[] args)
        {
            var input = Console.ReadLine ().Split (' ');
            var n = int.Parse (input[0]);
            var k = int.Parse (input[1]);
            var a = 0;
            if (n % 2 == 0)
                a = n / 2;

            else
                a = n / 2 + 1;

            if (a >= k)
                Console.WriteLine ("YES");

            else
                Console.WriteLine ("NO");
        }
    }
}