1870A - MEXanized Array - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;

int main()
{
    int T, i, j;
    cin >> T;
    while (T--)
    {
        int n, x, k;
        cin >> n >> x >> k;
        int sum = 0;

        for (i = 0; i < x; i++)
        {
            sum += i;
            n--;
        }

        if (n < 0 || x - 1 > k)
        {
            cout << -1 << endl;
        }
        else if (k == x)
        {
            sum += (n * (k - 1));
            cout << sum << endl;
        }
        else
        {
            sum += (n * k);
            cout << sum << endl;
        }
    }
    return 0;
}