#include <cstdio>
#include <iostream>
#define MAX 1012
#define LL long long
#define BOUND 955049953
using namespace std;

int T, N;
long long P[MAX];
long long R[MAX];

long long modinv(long long a, long long b){
	long long b0 = b, t, q;
	long long x0 = 0, x1 = 1;
	if (b == 1) return 1;
	while (a > 1) {
		q = a / b;
		t = b, b = a % b, a = t;
		t = x0, x0 = x1 - q * x0, x1 = t;
	}
	if (x1 < 0) x1 += b0;
	return x1;
}

// a * k + eq_c = eq_r (mod M)
long long solv(long long eq_a, long long eq_c, long long M, long long eq_r){


	//cout << eq_a << " * k + " << eq_c << " = " << eq_r << " (mod " << M << ")" << endl;

	long long k = (eq_r - eq_c) * modinv(eq_a, M);
	k %= M;
	if (k < 0){ k += M; }

	//cout << "k = " << k << endl;

	return eq_a * k + eq_c;
}

int main(){

	ios::sync_with_stdio(false);

	cin >> T;
	while(T--){
 		cin >> N;
 		for(int i = 0; i < N; ++i){ cin >> P[i] >> R[i]; }

		long long res = R[0];
		long long C = P[0];

		bool breakflag = 0;

		for(int i = 1; i < N; ++i){
			res = solv(C, res, P[i], R[i]);
			if(res < 0){ res += P[i]; }

			if (res >= BOUND) { breakflag = 1; break; }
			C *= P[i];
		}

		if(breakflag){ cout << "-1" << endl; } else { cout << res << endl; }

	}
	return 0;
}