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

ans = 0

n.times do |i|
  if a[i] == b[i] 
    if b[i] == c[i]
      next
    else
      ans += 1
    end
  else # a[i] != b[i]
    if a[i] == c[i]
      ans += 1
    elsif b[i] == c[i]
      ans += 1
    else
      ans += 2
    end
  end
end

puts ans
