int d7p2(const string& filename)
{
    ifstream file(filename);
    string line;
    getline(file, line);
    stringstream iss(line);

    vector<int> crabs;
    int sum = 0;
    for (int number; iss >> number;)
    {
        crabs.push_back(number);
        sum += number;
        if (iss.peek() == ',')
            iss.ignore();
    }
    int mean = (int)round(sum / crabs.size());

    int fuel = 0;
    for (const auto& crab : crabs)
    {
        int n = (int)abs(crab - mean);
        fuel += (int)(n * (n + 1) / 2);
    }
    return fuel;
}