Kr, Kb = gets.split.take(2).map(&:to_i)
S = gets.chomp

def valid?(s)
  !s.size.times.any?{|i|
    case s[i]
    when ?R
      i - Kr >= 0 && s[i - Kr] == ?R
    when ?B
      i - Kb >= 0 && s[i - Kb] == ?B
    end
  }
end

$memo = {}
$ans = 12
def f(s)
  n = s.size
  $memo[s] ||= if valid?(s) || n <= $ans
    $ans = [$ans, n].max
  else
    n.times.map{|i|
      t = s[0...i] + s[i + 1..-1]
      f(t)
    }.max
  end
end

p f(S)