n=gets.to_i
a=gets.chomp.split("")
b=gets.chomp.split("")
c=gets.chomp.split("")
cnt = 0
p n,a,b,c
for i in 0..n-1
	if a[i] != b[i] && a[i] != c[i] && b[i] != c[i] then
		cnt += 2
	elsif a[i] != b[i] || a[i] != c[i] || b[i] != c[i] then
		cnt +=1
	end
end
puts cnt