mx = 10**7 + 10
mf = [i for i in range(mx)]
for i in range(2, mx):
    if mf[i] != i:
        continue
    j = 2 * i
    while j < mx:
        mf[j] = i
        j += i

pr = []
for i in range(2, mx - 1):
    if mf[i] == i and mf[i + 2] == i + 2:
        pr.append(i)

t = int(input())
for _ in range(t):
    n = int(input())
    if n < 15:
        print(-1)
        continue
    ok = 0
    ng = len(pr)
    while (ng - ok) > 1:
        mid = (ok + ng) // 2
        if pr[mid] * (pr[mid] + 2) <= n:
            ok = mid
        else:
            ng = mid
    print(pr[ok] * (pr[ok] + 2))