n = read_line.to_i
s = read_line
cnt = 0
cnt_bb = 0
(n-1).times do |i|
    cnt += 1  if i < n-2 && s[i] == 'B' && s[i+1] == 'A' && s[i+2] == 'B'
    cnt_bb += 1 if s[i] == 'B' && s[i+1] == 'B'
end
ans = n- 1 -cnt
ans -= cnt_bb - 1 if cnt_bb > 0
puts ans