dot.cpp

#include <bits/stdc++.h>

using namespace std;

int main() {
  int t;
  cin >> t;
  while (t--) {
    int n, k, x;
    cin >> n >> k >> x;
    if (min(n, x + 1) < k) {
        cout << "-1\n";
        continue;
    }
    if (x == k) x--;
    cout << k*(k-1)/2 + x*(n-k) << "\n";
  }
}