Project Euler - Multiple of 3 and 5

    #include <iostream>
    using namespace std;
    int main()
    {
        int t;
        cin >> t;
        while (t--) {
            long long int n, x, y, z, m3, m5, m15, sum = 0;
            cin >> n;
            if (n % 3 == 0)
                x = (n - 1) / 3;
            else
                x = n / 3;
            if (n % 5 == 0)
                y = (n - 1) / 5;
            else
                y = n / 5;
            if (n % 15 == 0)
                z = (n - 1) / 15;
            else
                z = n / 15;

            m3 = (x * ((2 * 3) + (x - 1) * 3)) / 2;
            m5 = (y * ((2 * 5) + (y - 1) * 5)) / 2;
            m15 = (z * ((2 * 15) + (z - 1) * 15)) / 2;
            sum = m3 + m5 - m15;
            cout << sum << endl;
            sum = 0;
        }
        return 0;
    }