N = gets.chomp.to_i
A = gets.chomp
B = gets.chomp
C = gets.chomp
count = 0
0.upto(N-1) do |n|
  match = [A[n], B[n], C[n]].uniq.size
  if match == 2
    count += 1
  elsif match == 3
    count += 2
  end
end
puts count