def getscore(a, b, c)
  if a == b && b == c && a == c
    return 0
  elsif a != b && b != c && a != c
    return 2
  else
    return 1
  end 
end
# puts getscore('e', 'a', 'a')
n = gets.chomp.to_i
a = gets.chomp.split('')
b = gets.chomp.split('')
c = gets.chomp.split('')
sum = 0
for i in (0..(n-1))
  score = getscore(a[i], b[i], c[i])
  sum += score
end

puts sum