#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#include <bitset>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii; typedef long long ll;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

template<typename T>T gcd(T x, T y){if(y==0)return x;else return gcd(y,x%y);}

//template<typename Num>
typedef int Num;
bool reduceLCE(vector<pair<Num,Num> > equations, vector<pair<Num,Num> > &res) {
	int n = equations.size();
	res.clear(); res.reserve(n);
	for(int i = 0; i < n; ++ i) {
		pair<Num,Num> p = equations[i];
		if(p.first == 1) continue;

		for(int j = i+1; j < n; ++ j) {
			pair<Num,Num> &q = equations[j];
			int g = gcd(p.first, q.first);
			if((p.second - q.second) % g != 0) {
				res.clear();
				return false;
			}
			if(g > 1) {
				p.first /= g, q.first /= g;
				for(int h; (h = gcd(p.first, g)) != 1; ) {
					p.first *= h;
					g /= h;
				}
				q.first *= g;

				p.second %= p.first;
				q.second %= q.first;
			}
		}
		res.push_back(p);
	}
	return true;
}

int inverse(signed a, const int MOD) {
	a %= MOD;
	if(a < 0) a += MOD;
	signed b = MOD, u = 1, v = 0;
	while(b) {
		signed t = a / b;
		a -= t * b; swap(a, b);
		u -= t * v; swap(u, v);
	}
	if(u < 0) u += MOD;
	return u;
}

//prefix[i] = CRT(pairs[0..i-1]) mod pairs[i].first を求める
//
//pairsの一番後ろに(Mod,-1)を追加しておくことによって
//	CRT(pairs) mod Mod を求めることができる
//gcd(pairs[i].first, pairs[j].first) == 1 for i≠j を仮定する
//さらに、pairs[i].first > 1 も仮定する！
void prefixCRT(const vector<pair<int,int> > &pairs, vector<int> &prefixes) {
	int n = pairs.size();
	vector<int> ts(n);
	for(int i = 0; i < n; ++ i) {
		int m = pairs[i].first, x = 1;
		for(int j = 0; j < i; ++ j)
			x = (long long)x * pairs[j].first % m;
		ts[i] = inverse(x, m);
	}
	prefixes.resize(n);
	for(int i = 0; i < n; ++ i) {
		int m = pairs[i].first;
		int n1 = 1, a = 0;
		for(int j = 0; j < i; ++ j) {
			int n2 = pairs[j].first, a2 = pairs[j].second;
			int h = (long long)(a2 - prefixes[j]) * ts[j] % n2;
			if(h < 0) h += n2;
			a = (a + (long long)n1 * h) % m;
			n1 = (long long)n1 * pairs[j].first % m;
		}
		prefixes[i] = a;
	}
}

int main() {
	int N;
	scanf("%d", &N);
	vector<pii> equations;
	rep(i, N) {
		int X, Y;
		cin >> X >> Y;
		equations.push_back(mp(Y, X));
	}
	vector<pair<int,int> > pairs;
	bool ok = reduceLCE(equations, pairs);
	if(!ok) {
		puts("-1");
		return 0;
	}
	const int Mod = 1000000007;
	pairs.push_back(make_pair(Mod, -1));
	vector<int> prefixes;
	prefixCRT(pairs, prefixes);
	int ans = prefixes.back();

	bool zero = true;
	rep(i, pairs.size() - 1)
		zero &= pairs[i].second == 0;
	if(zero) {
		int prod = 1;
		rep(i, pairs.size() - 1)
			prod = (ll)prod * pairs[i].first % Mod;
		ans += prod;
	}

	printf("%d\n", ans);
	return 0;
}