N = gets.to_i
S = gets.chomp.chars.map(&:to_i)

ans = 0
counter = Hash.new(0)

S.each do |s|
  if s != 1 && s != 9
    ans += 1
  elsif s == 1
    counter[s] += 1
  elsif s == 9
    if counter[1] > 0
      counter[1] -= 1
      ans += 1
    else
      counter[s] += 1
    end
  end
end

if counter[9] >= 2 && counter[1] >= 1
  a = counter[9] / 2
  b = counter[1]
  c = [a, b].min

  ans += c
  counter[9] -= 2 * c
  counter[1] -= c
end

if counter[1] >= 2
  ans += counter[1] / 2
end

puts ans