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 Ruby (2.3.3) (judge verdict: Accepted)

#
# File    : A.rb
# Author  : Kazune Takahashi
# Created : 2/9/2019, 8:50:44 PM
# Powered by Visual Studio Code
#

n, k = gets.chomp.split(" ").map{|i| i.to_i}
ary = []
for i in 1..n
  if ary.empty? || i - ary[-1] > 1
    ary << i
  end
end
if ary.size >= k
  puts "YES"
else
  puts "NO"
end