INF = 10**100;
IDEN = (0, -INF);

def mul(a, b):
  return (a[0] + b[0], max(a[1], a[0] + b[1]));

def power(a, e):
  if (e == 0):
      return IDEN;
  if (a[0] > 0):
      return (e * a[0], (e - 1) * a[0] + a[1]);
  return (e * a[0], a[1]);

# y^f(0) x y^(f(1)-f(0)) x y^(f(2)-f(1)) x ... x y^(f(n)-f(n-1))
#   where f(i) = floor((a i + b) / m)
def pathUnder(m, a, b, n, e, x, y):
  c = (a * n + b) // m;
  pre = e;
  suf = e;
  while True:
    p = a // m; a %= m; x = mul(x, power(y, p));
    q = b // m; b %= m; pre = mul(pre, power(y, q));
    c -= (p * n + q);
    if (c == 0):
        return mul(mul(pre, power(x, n)), suf);
    d = (m * c - b - 1) // a + 1;
    suf = mul(mul(y, power(x, n - d)), suf);
    b = m - b - 1 + a;
    m, a = a, m;
    n = c - 1;
    c = d;
    x, y = y, x;

numCases = int(input());
for caseId in range(numCases):
    D, A, B, K = [int(_) for _ in input().split()];
    P = A * B // D;
    Q = B;
    
    def check(n):
        sm, mx = pathUnder(A, D, 0, n, IDEN, (Q, 0), (-P, -INF));
        return (mx > Q * K);
    
    lo = 0;
    hi = A * (Q * K + 1);
    if (check(hi)):
        while (lo + 1 < hi):
            mid = (lo + hi) // 2;
            if (check(mid)):
                hi = mid;
            else:
                lo = mid;
        print(D * lo);
    else:
        print(-1);