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

ans = 0

(0...n).each do |i|
    if a[i] != b[i]
        ans += 1
        if a[i] != c[i] and b[i] != c[i]
            ans += 1
        end
    elsif b[i] != c[i]
        ans += 1
    elsif a[i] != c[i]
        ans += 1
    end
end

puts ans