from math import gcd
INF = 10**2000
def mwf(n, m, a, b, c, d: int) -> int:
    def eval(m, a, b, c, d, x: int) -> int:
        return a * x + b * ((c * x + d) // m)
    ans = 0
    param = (n, m, a, b, c, d)
    ops = []
    def f(ans, param):
        n, m, a, b, c, d = param
        if n <= 0:
            ans = -INF
            return (True, ans, param)
        if c < 0 or d < 0:
            ops.append(("+", b * (d // m)))
            param = (n, m, a + b * (c // m), b, c % m, d % m)
            return (False, ans, param)
        if a >= 0 and b >= 0:
            ans = eval(m, a, b, c, d, n-1)
            return (True, ans, param)
        if a < 0 and b < 0:
            ans = eval(m, a, b, c, d, 0)
            return (True, ans, param)
        if m == 1:
            ans = max(eval(m, a, b, c, d, 0), eval(m, a, b, c, d, n-1))
            return (True, ans, param)
        if c >= m:
            c1 = c // m
            c2 = c % m
            param = (n, m, a + b * c1, b, c2, d)
            return (False, ans, param)
        if d >= m:
            d1 = d // m
            d2 = d % m
            param = (n, m, a, b, c, d2)
            ops.append(("+", b * d1))
            return (False, ans, param)
        k = (c * (n-1) + d) // m
        if a < 0:
            ops.append(("max", eval(m, a, b, c, d, 0)))
            ops.append(("+", b))
            param = (k, c, b, a, m, m - d + c - 1)
            return (False, ans, param)
        ops.append(("max", eval(m, a, b, c, d, n-1)))
        param = (k, c, b, a, m, m - d - 1)
        return (False, ans, param)
    while True:
        b, ans, param = f(ans, param)
        if b: break
    for op, val in ops[::-1]:
        if op == "+":
            ans = ans + val
        else:
            ans = max(ans, val)
    # print(ans)
    return ans

def solve():
    d, a, b, k = map(int, input().split())
    th = a * b * k * 2 + 4
    ng = 0
    ok = 1
    m = (a * b) // d
    while ok < th and mwf(ok+1, a, b, -m, d, 0) <= b * k:
        ok *= 2
    if ok >= th:
        print(-1)
        return
    while ok - ng > 1:
        mid = (ok + ng) // 2
        if mwf(mid+1, a, b, -m, d, 0) <= b * k:
            ng = mid
        else:
            ok = mid
    print(ok * d)

t = int(input())
for _ in range(t): solve()