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

total = 0
(0...n).each do |i|
  cnt = if a[i] == b[i] && b[i] == c[i]
	    	0
	  	elsif a[i] != b[i] && b[i] != c[i] && c[i] != a[i]
	    	2
  		else
	    	1
  		end
	total += cnt
end

puts total
