n = gets.to_i
a = gets.chomp
b = gets.chomp
c = gets.chomp

count = 0
n.times do |i|
  # same
  if a[i] == b[i] && b[i] == c[i]
    next
  end

  # only c
  if a[i] == b[i]
    count += 1
    next
  end

  # only b
  if a[i] == c[i]
    count += 1
    next
  end

  # only a
  if b[i] == c[i]
    count += 1
    next
  end

  count += 2
end

puts count
