#include <bits/stdc++.h>
using namespace std;
long long int gcd(long long int a, long long int b) {
  return (b == 0LL ? a : gcd(b, a % b));
}
long double dist(long double x, long double arayikhalatyan, long double x2,
                 long double y2) {
  return sqrt((x - x2) * (x - x2) +
              (arayikhalatyan - y2) * (arayikhalatyan - y2));
}
long long int S(long long int a) { return (a * (a + 1LL)) / 2; }
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
char vow[] = {'a', 'e', 'i', 'o', 'u'};
int dx[] = {0, -1, 0, 1, -1, -1, 1, 1, 0};
int dy[] = {-1, 0, 1, 0, -1, 1, -1, 1, 0};
const int N = 1e6 + 30;
const long long int mod = 1e9 + 7;
const long double pi = acos(-1);
const int T = 238;
const long double e = 1e-13;
long long int bp(long long int a, long long int b = mod - 2LL) {
  long long int ret = 1;
  while (b) {
    if (b & 1) ret *= a, ret %= mod;
    a *= a;
    a %= mod;
    b >>= 1;
  }
  return ret;
}
ostream& operator<<(ostream& c, pair<int, int> a) {
  c << a.first << " " << a.second;
  return c;
}
struct pt {
  long long int x, y;
  int ind;
  int bl;
  bool operator==(const pt& a) { return ind == a.ind; }
  bool operator<(const pt& b) {
    if (x == b.x) return y < b.y;
    return x < b.x;
  }
};
int x;
long long int a, b, c, d;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ;
  cin >> x;
  while (x--) {
    cin >> a >> b >> c >> d;
    if (b * c < a) {
      cout << -1 << endl;
      continue;
    }
    long long int t = a / b;
    t /= d, t *= d;
    long long int qn = t / d + 1;
    long long int sum = qn * a;
    long long int s = qn * t * b - S(qn - 1) * b * d;
    cout << sum - s << endl;
  }
  return 0;
}
