#include<bits/stdc++.h>
using namespace std;
int modinv(int a,int m){
	a%=m;
	if((a-1)%m==0)return a;
	return(1-(long)m*modinv(m,a))/a;
}
pair<int,int>crt_mod(vector<int>r,vector<int>m,int mod){
	int n=r.size();
	assert(m.size()==n);
	for(int i=1;i<n;i++)for(int j=0;j<i;j++){
		int g=gcd(m[i],m[j]);
		if((r[i]-r[j])%g)return{0,0};
		if(g==1)continue;
		m[i]/=g,m[j]/=g;
		int gi=gcd(m[i],g),gj=g/gi;
		do{g=gcd(gi,gj),gi*=g,gj/=g;}while(g!=1);
		m[i]*=gi,m[j]*=gj;
		assert(gcd(m[i],m[j])==1);
		r[i]%=m[i],r[j]%=m[j];
	}
	m.push_back(mod);
	vector<int>x(n+1),p(n+1,1);
	for(int i=0;i<n;i++){
		int k=long(r[i]-x[i])%m[i]*modinv(p[i],m[i])%m[i];
		if(k<0)k+=m[i];
		assert(0<=k&&k<m[i]);
		for(int j=i+1;j<=n;j++){
			x[j]=(x[j]+(long)k*p[j]%m[j])%m[j];
			p[j]=(long)p[j]*m[i]%m[j];
		}
	}
	return{x[n],p[n]};
}
int main(){
	int n;
	cin>>n;
	vector<int>r(n),m(n);
	for(int i=0;i<n;i++)cin>>r[i]>>m[i];
	auto[x,l]=crt_mod(r,m,1000000007);
	if(l==0){cout<<-1<<'\n';return 0;}
	bool zero=1;
	for(int i=0;i<n;i++)if(r[i]>0)zero=0;
	cout<<(zero?l:x)<<'\n';
}