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;
             
public static class Program
{
    public static void Main()
    {
        int[] R = GetIntArray();
        int N = R[0];
        int K = R[1];
	if (K == 1)
	{
		Console.WriteLine("YES");
		return;
        }
	Console.WriteLine(2 * K <= N + 1? "YES": "NO");
    }
    
    private static string ReadLine()
    {
    	return Console.In.ReadLine();
    }
    
    public static int[] GetIntArray()
    {
    	List<int> temp = new List<int>();
    	foreach (string c in ReadLine().Split(' '))
            temp.Add(int.Parse(c));
        return temp.ToArray();
    }
    
    public static int GetInt()
    {
    	return int.Parse(ReadLine());
    }
}