# frozen_string_literal: true

N, K = gets.chomp.split.map(&:to_i)
AS = gets.chomp.split.map(&:to_i)

if AS[K - 1].zero?
  puts(0)
  exit
end

count = 0
[AS[K..-1], AS[0..K - 1].reverse].each do |a|
  a.take_while do |i|
    if i >= 2
      count += i
      true
    elsif i == 1
      count += 1
      false
    else false
    end
  end
end

puts count