import java.util.Arrays;
import java.util.Scanner;

class Scratch {

	public static long mod_inv(long a, long m){
		return (a == 1 ? 1 : (1 - m*mod_inv(m%a, a)) / a + m);
	}

	public static long gcd(long a, long b){
		return b == 0 ? a : gcd(b, a % b);
	}

	public static boolean make_so(long[] as, long[] ms){
		while(true) {
			boolean updated = false;

			for (int fst = 0; fst < ms.length; fst++) {
				for (int snd = fst + 1; snd < ms.length; snd++) {
					long gcd = gcd(ms[fst], ms[snd]);
					if (gcd == 1) {
						continue;
					}

					updated = true;

					if (as[fst] % gcd != as[snd] % gcd) {
						return false;
					}

					ms[fst] /= gcd;
					ms[snd] /= gcd;
					while (true) {
						long gt = gcd(ms[fst], gcd);
						if (gt == 1) {
							break;
						}

						ms[fst] *= gt;
						gcd /= gt;
					}
					ms[snd] *= gcd;

					as[fst] %= ms[fst];
					as[snd] %= ms[snd];
				}
			}

			if(!updated){
				break;
			}
		}

		return true;
	}

	public static long chinese_remainder(long[] as, long[] ms){
		long[] vs = new long[ms.length];
		long[] sums = new long[ms.length];
		long[] invs = new long[ms.length];

		for(int i = 0; i < ms.length; i++){

			invs[i] = 1; // mod(ms[i]) の中で 1 / (ms[0] * ms[1] ... ms[i - 1]) を求める
			sums[i] = as[i]; // mod(ms[i]) の中で, a[i] - v[0] - v[1]ms[0] ... を求める
			long mult = 1; // mod(ms[i]) の中で, ms[0] * ... * ms[i - 2] を求める
			for(int j = 0; j < i; j++){
				sums[i] -= (vs[j] * mult) % ms[i];
				if(sums[i] < 0){ sums[i] += ms[i]; }

				invs[i] = (invs[i] * mod_inv(ms[j], ms[i])) % ms[i];
				mult = (mult * ms[j]) % ms[i];
			}

			vs[i] = (sums[i] * invs[i]) % ms[i];
		}

		boolean flg = true;
		for(int i = 0; i < ms.length; i++){
			if(vs[i] != 0){ flg = false; break;}
		}

		if(flg){
			long prod = 1;
			for(final long p : ms){
				prod *= p;
				prod %= 1000000007;
			}

			return prod;
		}

		long ret = 0;
		for(int i = 0; i < ms.length; i++){
			long mult = 1;
			for(int j = 0; j < i; j++){ mult *= ms[j]; mult %= 1000000007;}// ここで MOD が必要な場合は取る
			ret += vs[i] * mult;// ここで MOD が必要な場合は取る
			ret %= 1000000007;
		}

		return ret;
	}

	public static void main(String[] args) {
		try (Scanner sc = new Scanner(System.in)) {
			final int N = sc.nextInt();

			long[] as = new long[N];
			long[] ms = new long[N];
			for (int i = 0; i < N; i++){
				as[i] = sc.nextLong();
				ms[i] = sc.nextLong();
			}

			final boolean so = make_so(as, ms);
			//System.out.println(Arrays.toString(as));
			//System.out.println(Arrays.toString(ms));
			if(!so){
				System.out.println(-1);
				return;
			}

			long prod = 1;
			for(final long p : ms){
				prod *= p;
				prod %= 1000000007;
			}

			final long ret = chinese_remainder(as, ms);
			System.out.println(ret);
		}
	}
}