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

split_words_a = a.split("")
split_words_b = b.split("")
split_words_c = c.split("")
i = 0
ancer = 0

n.times do
  if split_words_a[i] == split_words_b[i] && split_words_b[i] == split_words_c[i]
    next
  elsif split_words_a[i] == split_words_b[i]
    ancer += 1
  elsif split_words_a[i] == split_words_c[i]
    ancer += 1
  elsif split_words_b[i] == split_words_c[i]
    ancer += 1
  else
    ancer += 2
  end
  i += 1
end


puts ancer