n = gets.to_i
strs = Array.new(3) { gets.chomp }
sum = 0
n.times do |i|
  a = strs[0][i]
  b = strs[1][i]
  c = strs[2][i]

  sum += if a == b && b == c
           0
         elsif a == b || b == c || c == a
           1
         else
           2
         end
end
puts(sum)