def eratosthenes(n):
    primes = [True] * (n+1)
    primes[0], primes[1] = False, False
    for i in range(2, int(n**0.5)+1):
        if primes[i]:
            for j in range(i*i, n+1, i):
                primes[j] = False

    twins = []
    for i in range(2, n - 1):
        if primes[i] and primes[i+2]:
            twins.append(i)

    return twins

t = int(input())
for _ in range(t):
    n = int(input())
    primes_list = list(eratosthenes(n))

    ok, ng = -1, len(primes_list)
    while abs(ok - ng) > 1:
        mid = (ok + ng) // 2
        p = primes_list[mid]
        if p * (p + 2) <= n:
            ok = mid
        else:
            ng = mid

    if ok == -1:
        print(-1)
    else:
        print(primes_list[ok] * (primes_list[ok] + 2))