n = gets.to_i
s = gets.chomp
size = s.size
div, mod = s.size.divmod(2)
ans = 0
until ans != 0
  0.upto(mod).each do |f_start|
    (f_start + div).upto(size - div).each do |l_start|
      if s[f_start, div] == s[l_start, div]
        ans = div
      end
    end
  end
  if ans != 0
    break
  else
    div -= 1
    mod += 2
  end
end
puts ans == -1 ? 0 : ans
