#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
LL exgcd(LL a,LL b,LL &x,LL &y){
if(b==0){
x=1,y=0;
return a;
}
LL d=exgcd(b,a%b,y,x);
y-=a/b*x;
return d;
}
int main(){
int n;
LL x=0;
cin>>n;
LL m1,a1;
cin>>a1>>m1;
for(int i=0;i<n-1;i++){
LL a2,m2,k1,k2;
cin>>a2>>m2;
LL d=exgcd(a1,a2,k1,k2);
if((m2-m1)%d){x=-1;break;}
k1*=(m2-m1)/d;
k1=(k1%(a2/d)+a2/d)%(a2/d);
x=k1*a1+m1;
LL m=abs(a1/d*a2);
m1=k1*a1+m1;
a1=m;
}
if(x!=-1)x=(m1%a1+a1)%a1;
cout<<x<<endl;
return 0;
}