def sol d, s
    f = 'x'
    c = 0
    a = []
    15.times{|i|
        if s[i] == f
            c += 1
        else
            a.push(c)
            f = s[i]
            c = 1
        end
        }
    a.push(c)
    if a.size == 1
        return d
    else
        a.pop
        a.shift
        ans = [a[0] + d, a[-1] + d].max
        a.size.times{|i|
            if i % 2 == 0
                next
            end
            if a[i] > d
                ans = [ans, a[i - 1] + d, a[i + 1] + d].max
            else
                ans = [ans, a[i - 1] + a[i] + a[i + 1]].max
            end
            }
        return ans
    end
end

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