#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

std::vector<int> sieve(int n) {
	std::vector<int> res;
	std::vector<bool> is_prime(n + 1, true);
	is_prime[0] = is_prime[1] = false;
	for (int i = 2; i * i <= n; i++) {
		if (!is_prime[i]) continue;
		for (int j = i * i; j <= n; j += i) is_prime[j] = false;
	}
	for (int i = 2; i <= n; ++i) if (is_prime[i]) res.emplace_back(i);
	return res;
}

namespace tk {
template<typename T>
T mod_pow(T x, T n, const T & mod) {
	assert(mod > 0);
	assert(n >= 0);
	x = (x % mod + mod) % mod;
	T res = 1 % mod;
	while (n > 0) {
		if (n & 1) res = res * x % mod;
		x = x * x % mod;
		n >>= 1;
	}
	return res;
}
} // namespace tk


int main() {
	int T;
	cin >> T;
	
	auto prime = sieve(5000000);
	
	while (T--) {
		ll A, P;
		scanf("%lld %lld", &A, &P);
		
		auto it = lower_bound(ALL(prime), P);
		if (it == prime.end() || *it != P) { puts("-1"); continue; }
		else if (P == 2) printf("%lld\n", A % P);
		else puts("1");
	}
}