N = gets.to_i
S = gets.chomp

if S.each_char.all?(?.)
    puts 0
    exit
end

last = -2
(0 ... N).reverse_each do |i|
    c = S[i]
    next if c == ?.
    d = N - i - 1
    
    if last + 1 >= d
        d = last + 2
    end
    
    last = d
end

puts last + 1