#include <cmath>

 #include <cstdio>

 #include <cstring>

 #include <algorithm>

 #define ll long long

 #define N 100010

 #define rint register int

 #define ll long long

 #define il inline

 using namespace std;

 //re

 int n;

 ll A[N],B[N];

 ll qadd(ll x,ll y,const ll &mo){ll ans=;while(y){if(y&)ans=(ans+x)%mo;x=(x+x)%mo;y>>=;}return ans;}

 ll qpow(ll x,ll y,const ll &mo){ll ans=;while(y){if(y&)ans=(ans*x)%mo;x=(x*x)%mo;y>>=;}return ans;}

 ll exgcd(ll a,ll b,ll &x,ll &y){

     if(b==){x=,y=;return a;}

     ll ans=exgcd(b,a%b,x,y);

     ll t=x;x=y;y=t-a/b*y;

     return ans;

 }

 ll excrt()

 {

     ll x,y,ans=A[],M=B[],bg;

     for(int i=;i<=n;i++)

     {

         ll a=M,b=B[i],c=(A[i]-ans%b+b)%b;

         ll gcd=exgcd(M,b,x,y);bg=b/gcd;

         if(c%gcd!=) return -;

         x=qadd(x,c/gcd,bg);

         ans+=x*M;

         M*=bg;

         ans=(ans%M+M)%M;

     }

     return ans;

 }

 int main()

 {

     scanf("%d",&n);

     for(int i=;i<=n;i++)

         scanf("%lld%lld",&B[i],&A[i]);

     printf("%lld\n",excrt());

     return ;

 }