N, K = gets.split.map(&:to_i)
def f(n, k)
  @dp ||= {}
  @dp[[n, k]] ||= if n == 1
                    0
                  else
                    [1, k-1].min + ((k + 1)..n).map{|i| f(n - 1, i - 1)}.inject(0, :+)
                  end
end
ans = f(N, K)
puts ans