import sys
import os


IS_LOCAL = os.environ.get("LOCAL") == "true"


def debug(*args, sep=" ", end="\n", flush=False) -> None:
    if IS_LOCAL:
        print(*args, sep=sep, end=end, file=sys.stderr, flush=flush)


def yn(flg: bool) -> bool:
    print('Yes' if flg else 'No')
    return flg


def gcd(a, b):
    a = abs(a); b = abs(b)
    if a < b: a, b = b, a
    while b > 0:
        a, b = b, a % b
    return a


def lcm(a, b):
    return a * b // gcd(a, b)


def isqrt(N):
    res = int(N**0.5) + 3
    while res * res > N:
        res -= 1
    return res


def main():
    readline = sys.stdin.readline

    T = int(input())
    for _ in range(T):
        N, K = map(int, readline().split())
        if N == K:
            print(-1)
            continue
        if N > K * K:
            print(N)
            continue
        m = N // K
        s = isqrt(N)
        seen = [False] * s
        for a in range(m, s):
            i = N - a * (N // a)
            if i < s:
                seen[i] = True
        for b in range(1, s + 1):
            a = min(N // b, K)
            i = N - a * b
            if i < s:
                seen[i] = True
        for i in range(s):
            if not seen[i]:
                print(N - i)
                break


if __name__ == "__main__":
    main()