package yukicoder;

import java.util.Scanner;

public class Main {

	private static final int MOD = 1000000007;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] X = new int[N];
		int[] Y = new int[N];
		for (int i = 0; i < N; i++) {
			X[i] = sc.nextInt();
			Y[i] = sc.nextInt();
		}

		for (int i = 1; i < N; i++) {
			int[] cmt = cmt(X[0], Y[0], X[i], Y[i]);
			if (cmt[0] < 0) {
				System.out.println(-1);
				return;
			}

			X[0] = cmt[0];
			Y[0] = cmt[1];
		}

		if (X[0] == 0) {
			X[0] = Y[0];
		}

		System.out.println(X[0]);
	}

	static int[] extgcd(int a, int b, int[] is) {
		if (a == 0) {
			is[0] = 0;
			is[1] = 1;
			is[2] = b;
		} else {
			extgcd(b % a, a, is);
			int x = is[1] - b / a * is[0];
			is[1] = is[0];
			is[0] = x;
		}
		return is;
	}

	static int[] cmt(int a1, int mo1, int a2, int mo2) {
		int[] exgcd = extgcd(mo1, mo2, new int[3]);
		int g = exgcd[2];
		int x = exgcd[0];

		a1 %= mo1;
		a2 %= mo2;
		if (a1 % exgcd[2] != a2 % exgcd[2]) {
			return new int[] { -1, 0 };
		}

		int lcm = mo1 * (mo2 / g);
		int v = a1 + ((a2 - a1) % lcm) * x % lcm * (mo1 / g);
		return new int[] { ((v % lcm) + lcm) % lcm, lcm };
	}

}