N = gets.to_i
A = gets.strip
B = gets.strip
C = gets.strip

count = 0

N.times{|i|
	a = A[i]
	b = B[i]
	c = C[i]
	
	chars = [a, b, c].sort.uniq
	
	if chars.length == 3
		count += 2
	elsif chars.length == 2
		count += 1
	end
	
}

puts count
