#ifdef LOCAL111
	#define _GLIBCXX_DEBUG
#else
	#define NDEBUG
#endif
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
const int INF = 1e9;
using namespace std;
template<typename T, typename U> ostream& operator<< (ostream& os, const pair<T,U>& p) { cout << '(' << p.first << ' ' << p.second << ')'; return os; }

#define endl '\n'
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#ifdef LOCAL111
	#define DEBUG(x) cout<<#x<<": "<<(x)<<endl
	template<typename T> void dpite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
#else
	#define DEBUG(x) true
	template<typename T> void dpite(T a, T b){ return; }
#endif
#define F first
#define S second
#define SNP string::npos
#define WRC(hoge) cout << "Case #" << (hoge)+1 << ": "
template<typename T> void pite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
template<typename T> bool chmax(T& a, T b){if(a < b){a = b; return true;} return false;}
template<typename T> bool chmin(T& a, T b){if(a > b){a = b; return true;} return false;}

template <typename T>
long long gcd(T x, T y){
	return y==0 ? x : gcd(y, x%y);
}

//res.first*a+res.second*b == 1 となるresを返す (a,bは互いに素)
pair<long long, long long> extgcd(long long a,long long b)
{
	if(b==1){
		return pair<long long, long long>(0,1);
	}
	pair<long long, long long> t=extgcd(b,a%b);
	return pair<long long, long long>(t.second,t.first-a/b*t.second);
}

//modの逆元を返す
long long inverse(long long a,long long modl)
{
	return (extgcd(modl,a).second+modl)%modl;
}

// x = second (mod first)
long long garner(const vector<pair<long long, long long>>& ex) {
	int n = ex.size();
	long long res = 0;
	long long k = 1;
	for(int i = 0; i < n; ++i) {
		DEBUG(i);
		DEBUG(res);
		long long x, m;
		tie(m,x) = ex[i];
		long long g = gcd(k,m);
		m /= g;
		k /= g;
		if((x-res)%g != 0) return -1;
		DEBUG(m);
		DEBUG(k);
		DEBUG((x-res)/g);
		long long inv = inverse(k,m);
		long long v = (x-res)/g*inv;
		DEBUG(v);
		res += v*k*g;
		k = k*m*g;
	}
	return res;
}

long long garner(const vector<long long>& x, const vector<long long>& mod){
	int n = x.size();
	vector<pair<long long, long long>> v(n);
	for(int i = 0; i < n; ++i) {
		v[i] = {mod[i],x[i]};
	}
	return garner(v);
}

long long use_garner(vector<long long>& x, vector<long long>& mod){
	int n = x.size();
	for(int i = 0; i < n; ++i) {
		x[i] %= mod[i];
	}
	if(n == 1) return x[0];
	long long g = gcd(mod[0],mod[1]);
	for(int i = 2; i < n; ++i) {
		g = gcd(g,mod[i]);
	}
	vector<pair<long long, long long>> ex(n);
	for(int i = 0; i < n; ++i) {
		mod[i] /= g;
		if(x[i]%g != 0) return -1;
		x[i] /= g;
		ex[i] = {mod[i],x[i]};
	}
	ex.erase(unique(ex.begin(), ex.end()),ex.end());
	for(int i = 0; i < n-1; ++i) {
		if(ex[i].first == ex[i+1].second) return -1;
	}
	dpite(ALL(ex));
	return garner(ex);
}

typedef long long int LL;
typedef unsigned long long ULL;
typedef pair<int,int> P;

void ios_init(){
	//cout.setf(ios::fixed);
	//cout.precision(12);
#ifdef LOCAL111
	return;
#endif
	ios::sync_with_stdio(false); cin.tie(0);	
}

int main()
{
	ios_init();
	int n;
	while(cin >> n) {
		vector<long long> x(n);
		vector<long long> y(n);
		REP(i,n) cin >> x[i] >> y[i];
		cout << garner(x,y) << endl;
	}
	return 0;
}