import sys

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for k in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for k in range(c)] for k in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10**9)
INF = 10**19
MOD = 10**9 + 7
EPS = 10**-10

def eratosthenes_sieve(n):
    """ 素数列挙(エラトステネスの篩) """

    table = [0] * (n+1)
    prime_list = []
    for i in range(2, n+1):
        if table[i] == 0:
            prime_list.append(i)
            for j in range(i+i, n+1, i):
                table[j] = 1
    return prime_list

primes = set(eratosthenes_sieve(5000000))

for _ in range(INT()):
    a, p = MAP()

    if p in primes:
        print(1)
    else:
        print(-1)