#include<iostream>
using namespace std;
#include<stdio.h>
long long  extend_gcd(long long a,long long b,long long  &x,long long  &y)
{
   long long ans,t;
    if(b==0){
		x=1;
		y=0;
		return a;}
    ans=extend_gcd(b,a%b,x,y);
	t=x;
	x=y;
	y=t-(a/b)*y;
    return ans;   
    }
int main()
{ 
 long long  k,a1,r1,a2,r2,x,y,gcd,t;
	
    bool flag;
    while(cin>>k)
    {
         scanf("%lld %lld",&a1,&r1);
          if(k==1)
          {
             if(a1<=r1)
				 cout<<-1;
             else cout<<r1;     
             }
          k--;
          flag=0;
          while(k--)
          {
                 scanf("%lld %lld",&a2,&r2);
                if(a2<=r2)flag=1;
                gcd=extend_gcd(a1,a2,x,y);
                if((r2-r1)%gcd!=0)flag=1;
                else
                { 
					t=a2/gcd;
                    x=((r2-r1)/gcd*x%t+t)%t;
                   
                    r1=x*a1+r1;
                    a1=a1*a2/gcd;//lcm(a1,a2);
                    r1=(r1%a1+a1)%a1;
                    
				}                        
                }        
          if(flag)
			  cout<<-1;
          else 
		  cout<<r1;                       
          }
    return 0;
    }