def chck(a, b):
    flg = True
    for i in range(a, 0, -1):
        for j in range(b, 0, -1):
            # print(i, j)
            if i%j==0 and i//j <= b:
                break
            if i%j==0 and i//j > b:
                print(i)
                return
            

t = int(input())
for x in range(t):
    a, b= map(int, input().split())
    if a==b: print(-1)
    else: chck(a,b)