import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**16
md = 998244353
# md = 10**9+7

class Sieve:
    def __init__(self, n):
        self.plist = [2]  # n以下の素数のリスト
        min_prime_factor = [2, 0] * (n // 2 + 5)
        for x in range(3, n + 1, 2):
            if min_prime_factor[x] == 0:
                min_prime_factor[x] = x
                self.plist.append(x)
                if x ** 2 > n: continue
                for y in range(x ** 2, n + 5, 2 * x):
                    if min_prime_factor[y] == 0:
                        min_prime_factor[y] = x
        self.min_prime_factor = min_prime_factor

    def isprime(self, x):
        return self.min_prime_factor[x] == x

def solve():
    a,p=LI()
    if sv.isprime(p):
        if a==p:print(0)
        else:print(1)
    else:print(-1)

sv=Sieve(5000001)
for _ in range(II()):
    solve()