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;
using System.Collections.Generic;
using System.Linq;
using static Input;

public class Prog
{
    private const int INF = 1000000007;
    public static void Main()
    {
        int N = NextInt();
        int K = NextInt();
        if (N % 2 == 1) N++;
        Console.WriteLine((N < K*2?"NO":"YES"));
    }
}

public class Input
{
    private static Queue<string> queue = new Queue<string>();
    private static void Confirm() { if (queue.Count == 0) foreach (var s in Console.ReadLine().Split(' ')) queue.Enqueue(s); }
    public static int NextInt() { Confirm(); return int.Parse(queue.Dequeue()); }
    public static long NextLong() { Confirm(); return long.Parse(queue.Dequeue()); }
    public static string NextString() { Confirm(); return queue.Dequeue(); }
    public static double NextDouble() { Confirm(); return double.Parse(queue.Dequeue()); }
    public static int[] LineInt() { return Console.ReadLine().Split(' ').Select(int.Parse).ToArray(); }
    public static long[] LineLong() { return Console.ReadLine().Split(' ').Select(long.Parse).ToArray(); }
    public static string[] LineString() { return Console.ReadLine().Split(' ').ToArray(); }
    public static double[] LineDouble() { return Console.ReadLine().Split(' ').Select(double.Parse).ToArray(); }
}