N, K = gets.split.map(&:to_i)
A = gets.split.map(&:to_i)
l = 0
r = N - 1

(1 .. N).find do |i|
  if i < K
    l = i - 1 if A[i - 1] <= 1
    false
  elsif i > K
    r = i - 1 if A[i - 1] <= 1
    true
  else
    false
  end
end

if A[K - 1] == 0
  puts 0
elsif A[K - 1] == 1
  puts [A[l .. K-1].inject(&:+), A[K-1 .. r].inject(&:+)].max
else
  puts A[l .. r].inject(&:+)
end