DBG = true
n = gets.to_i
a = gets.chomp
b = gets.chomp
c = gets.chomp
sum = 0
for i in 0...n
  if a[i] != b[i] && b[i] != c[i] && c[i] != a[i]
    sum += 2
  elsif a[i] != b[i] || b[i] != c[i] || c[i] != a[i]
    sum += 1
  end
end
puts "#{sum}"
