ProjectEuler -01 Multiple of 3 and 5

PROBLEM :  https://www.hackerrank.com/contests/projecteuler/challenges/euler001
If we list all the natural numbers below that are multiples of or , we get and . The sum of these multiples is .
Find the sum of all the multiples of or below .

Input Format

First line contains that denotes the number of test cases. This is followed by lines, each containing an integer, .

Constraints

Output Format

For each test case, print an integer that denotes the sum of all the multiples of or below .

Sample Input 0

2
10
100

Sample Output 0

23
2318

Explanation 0

For , if we list all the natural numbers below that are multiples of or , we get and . The sum of these multiples is .
Similarly for , we get .

Solution :

#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;
}