def getPrimes(last: int, first: int = 1):
    if last < first:
        last, first = first, last
    isPrime = [True] * (last + 1)
    isPrime[0] = isPrime[1] = False
    for i in range(2, int(last ** 0.5 + 1)):
        if isPrime[i]:
            for j in range(i ** 2, last + 1, i):
                isPrime[j] = False
    return [i for i in range(first, last + 1) if isPrime[i]] 
primes=set(getPrimes(int((10**9)**0.5)+1))
T=int(input())
for _ in range(T):
    N,K=map(int,input().split())
    if K==N:
        print(-1)
    else:
        ans=0
        for i in range(N,K,-1):
            if i in primes:
                ans=max(ans,i*(N//i))
        print(ans)