n = gets.to_i
a = gets.chomp
b = gets.chomp
c = gets.chomp
count = 0
for i in 0...n do
  if a[i] != b[i] && b[i] != c[i] && c[i] != a[i]
    count += 2
  elsif a[i] == b[i] && b[i] == c[i]
    count += 0
  else
    count += 1
  end
end
puts count
