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

ans = 0
for i in 0..(n - 1) do
  if a[i] != b[i] && b[i] != c[i]
    ans += 2
  elsif a[i] != b[i] || b[i] != c[i] || c[i] != a[i]
    ans += 1
  end
end

puts ans
