def holiday s
    s += 'x'
    tmp = ans = 0
    43.times{|i|
        if s[i] == 'o'
            tmp += 1
        else
            ans = [tmp, ans].max
            tmp = 0
        end
        }
    return ans
end

def sol d, s
    ans = 0
    (43 - d).times{|i|
        ans = [ans, holiday(s[0...i].to_s + 'o' * d + s[(i + d)..-1].to_s)].max
        }
    return ans
end

d = gets.to_i
s = STDIN.map(&:chomp).join('')
s = 'x' * 14 + s + 'x' * 14
p sol(d, s)