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;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Text;
using System.Threading.Tasks;
using static System.Console;
using static System.Math;
class Z { static void Main() => new K(); }
class K
{
    int F => int.Parse(Str);
    long FL => long.Parse(Str);
    int[] G => Strs.Select(int.Parse).ToArray();
    long[] GL => Strs.Select(long.Parse).ToArray();
    string Str => ReadLine();
    string[] Strs => Str.Split(new char[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries);
    const int MOD = 1000000007;
    public K()
    {
        SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
        Solve();
        Out.Flush();
    }
    void Solve()
    {
        var I = G;
        WriteLine(I[1] <= (1 + I[0]) / 2 ? "YES" : "NO");
    }
}