N = gets.to_i
S = gets.chomp
s = S.dup

checked = Hash.new
ans = 0

0.upto(N - 2) do |i|
  s[i] = 'B'
  s[i + 1] = 'B'

  if not checked[s]
    checked[s] = true
    ans += 1
  end

  s[i] = S[i]
  s[i + 1] = S[i + 1]

end

puts ans