#include <bits/stdc++.h>
using namespace std;
template <class c>
struct rge {
  c b, e;
};
template <class c>
rge<c> range(c i, c j) {
  return rge<c>{i, j};
}
template <class c>
auto dud(c* x) -> decltype(cerr << *x, 0);
template <class c>
char dud(...);
struct debug {
  ~debug() { cerr << endl; }
  template <class c>
  typename enable_if<sizeof dud<c>(0) != 1, debug&>::type operator<<(c i) {
    cerr << boolalpha << i;
    return *this;
  }
  template <class c>
  typename enable_if<sizeof dud<c>(0) == 1, debug&>::type operator<<(c i) {
    return *this << range(begin(i), end(i));
  }
  template <class c, class b>
  debug& operator<<(pair<b, c> d) {
    return *this << "(" << d.first << ", " << d.second << ")";
  }
  template <class c>
  debug& operator<<(rge<c> d) {
    *this << "[";
    for (auto it = d.b; it != d.e; ++it) *this << ", " + 2 * (it == d.b) << *it;
    return *this << "]";
  }
};
long double eps = (long double)1 / 1e6;
const long double pi = 3.14159265359;
long long inf = 1e18, mod1 = 1e9 + 7;
long long sqr(long long a) { return a * a; }
long long qb(long long a) { return a * a * a; }
template <typename T>
bool umax(T& a, T b) {
  return a < b ? a = b, 1 : 0;
}
template <typename T>
bool umin(T& a, T b) {
  return b < a ? a = b, 1 : 0;
}
bool is_prime(long long val) {
  for (long long i = 2; i <= sqrt(val); i++)
    if (val % i == 0) return 0;
  return 1;
}
long long gcd(long long a, long long b) { return !a ? b : gcd(b % a, a); }
long long binpow(long long a, long long b, long long mod) {
  return b ? (b % 2 ? (a * (sqr(binpow(a, b / 2, mod)) % mod)) % mod
                    : sqr(binpow(a, b / 2, mod)) % mod)
           : 1;
}
long long binmult(long long a, long long b, long long mod) {
  return b ? (b % 2 ? (2 * binmult(a, b / 2, mod) + a) % mod
                    : (2 * binmult(a, b / 2, mod)) % mod)
           : 0;
}
const long long RR = 1e4;
const long long tx[8] = {1, -1, 2, -2, -1, -2};
const long long ty[8] = {-2, -2, -1, -1, 2, 1};
const char rev_to[4] = {'E', 'W', 'N', 'S'};
const long long M = 998244353;
const long long ppp = 73;
const long long K = 2e5 + 2;
const long long block = 600;
const long long OPEN = 1;
const long long CLOSE = 0;
auto rnd =
    bind(uniform_int_distribution<long long>(1, 5969699), mt19937(time(0)));
void bad() {
  cout << "-1";
  exit(0);
}
long long a, b, c, d;
long long col(long long vl) { return (vl + 1) * vl / 2; }
long long first(long long t) {
  long long a1 = (a * ((t + d - 1) / d));
  long long cl = c / d;
  t--;
  if (cl * d <= t) {
    a1 -= col(cl) * d * b;
    t -= cl * d;
    long long kek = c % d * (cl + 1) + (d - c % d) * (cl);
    a1 -= t / d * kek * b;
    t %= d;
    a1 -= min(t, c % d) * b * (cl + 1);
    t -= min(t, c % d);
    a1 -= t * (cl)*b;
  } else {
    cl = (t) / d;
    a1 -= col(cl) * d * b;
    a1 -= max((long long)0, (t % d) * (cl + 1)) * b;
  }
  return a1;
}
signed main() {
  cin.tie(0);
  cout.tie(0);
  ios_base::sync_with_stdio(0);
  ;
  long long t;
  cin >> t;
  while (t--) {
    cin >> a >> b >> c >> d;
    long long l = 0, r = 1e6 / d;
    while (r - l > 3) {
      long long tl = l + (r - l) / 3;
      long long tr = r - (r - l) / 3;
      if (first(tl * d + 1) > first(tr * d + 1))
        r = tr;
      else
        l = tl;
    }
    long long ans = 0;
    for (long long i = l; i <= r; i++) {
      umax(ans, first(i * d + 1));
    }
    if (r == ((long long)1e6 / d) && first(l * d + 1) < first(r * d + 1) &&
        first(r * d + 1) < first((r + 1) * d + 1)) {
      ans = -1;
    }
    cout << ans << "\n";
  }
  return 0;
}
