#include <iostream>
using namespace std;using i128=__int128_t;long long exgcd(long long a,long long b,long long&x,long long&y){if(!b){x=1;y=0;return a;}long long g=exgcd(b,a%b,y,x);y-=a/b*x;return g;}
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n;while(cin>>n){long long r=0,M=1;bool ok=true;while(n--){long long m,b;cin>>m>>b;if(!ok)continue;long long x,y,g=exgcd(M,m,x,y),diff=b-r;if(diff%g){ok=false;continue;}long long mod=m/g,t=(i128)(diff/g)*x%mod;if(t<0)t+=mod;i128 nr=(i128)r+(i128)M*t;i128 nm=(i128)M/g*m;if(nm>(i128)9e18){ok=false;continue;}M=(long long)nm;r=(long long)(nr%M);if(r<0)r+=M;}cout<<(ok?r:-1)<<'\n';}}