int getMoneySpent(vector<int> keyboards, vector<int> drives, int b) {
    std::sort(keyboards.begin(), keyboards.end());
    std::sort(drives.begin(), drives.end());
    int maxSum = -1;
    for(int j = drives.size() - 1, i = 0; i < keyboards.size() && j >= 0;) {
        const int sum = keyboards[i] + drives[j];
        if (sum <= b) {
            if (sum > maxSum)
                maxSum = sum;
            i++;
        } else {
            j--;
        }
    }
    return maxSum;
}