using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Diagnostics;
using System.Numerics;
using Enu = System.Linq.Enumerable;

public class Program
{
    static readonly int Mod = (int)1e9 + 7;

    public void Solve()
    {
        int N = Reader.Int();
        long[] M = new long[N], A = new long[N];
        for (int i = 0; i < N; i++)
        {
            A[i] = Reader.Int(); M[i] = Reader.Int();
        }
        var ans = LinearCongruence(M, A);
        Console.WriteLine(ans == -1 ? -1 : ans % Mod);
    }

    // X % M[i] = A[i] 
    static BigInteger LinearCongruence(long[] M, long[] A, bool positive = true)
    {
        BigInteger x = 0, m = 1;
        for (int i = 0; i < A.Length; i++)
        {
            var a = m;
            var b = A[i] - x;
            var d = BigInteger.GreatestCommonDivisor(M[i], a);
            if (d == 0 || b % d != 0) return -BigInteger.One;
            var e = M[i] / d;
            var t = b / d * ModInverse(a / d, e) % e;
            x = x + m * t;
            m *= M[i] / d;
        }
        if (x == 0) return positive ? m : 0;
        return x > 0 ? x % m : x % m + m;
    }
    static BigInteger ModInverse(BigInteger x, BigInteger mod)
    {
        BigInteger y = mod, a = 1, b = 0, t;
        while (y != 0)
        {
            var d = x / y;
            t = x - d * y; x = y; y = t;
            t = a - d * b; a = b; b = t;
        }
        return a >= 0 ? a % mod : a % mod + mod;
    }
}


class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    static TextReader reader = Console.In;
    static readonly char[] separator = { ' ' };
    static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    static string[] A = new string[0];
    static int i;
    static void Init() { A = new string[0]; }
    public static void Set(TextReader r) { reader = r; Init(); }
    public static void Set(string file) { reader = new StreamReader(file); Init(); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Range(N, Int); }
    public static int[][] IntTable(int H) { return Range(H, IntLine); }
    public static string[] StringArray(int N) { return Range(N, Next); }
    public static string[][] StringTable(int N) { return Range(N, () => Split(Line())); }
    public static string Line() { return reader.ReadLine().Trim(); }
    public static T[] Range<T>(int N, Func<T> f) { var r = new T[N]; for (int i = 0; i < N; r[i++] = f()) ; return r; }
    static string[] Split(string s) { return s.Split(separator, op); }
    static string Next() { CheckNext(); return A[i++]; }
    static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}