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

ans = 0
n.times do |i|
    if a[i] == b[i] && a[i] == c[i]
        next
    elsif a[i] != b[i] && b[i] != c[i] && c[i] != a[i]
        ans += 2
    else
        ans += 1
    end
end

puts ans