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

dp = Array.new(N + 1, -1)
dp[N] = 0
len = Float::INFINITY

(N - 1).downto(0) do |i|
  if i != 0 && S[i - 1] == 'x'
    len += 1
  else
    if len > K - 1
      dp[i] = 1
      len = 0
    else
      len += 1
    end
  end
end

idx = dp.index(1)

if idx
  puts idx
else
  puts 0
end