n = gets.to_i
a = gets.chomp.chars
b = gets.chomp.chars
c = gets.chomp.chars
res = 0
(0...n).each do |i|
  next if a[i] == b[i] && b[i] == c[i]
  if a[i] != b[i] && b[i] != c[i] && c[i] != a[i]
    res += 2
  else
    res += 1
  end
end
puts res