#define?first?f
#define?second?s
#define?ll?long?long
#define?mp?make_pair
#define?pb?push_back
#include<bits/stdc++.h>
#define?pii?pair<ll,ll>
#define?mem(a,b)?memset(a,b,sizeof(a))
using?namespace?std;
const?int?maxn=2e5+5;

ll?a[maxn],r[maxn];
ll?ex_gcd(ll?a1,ll?b1,ll?&x,ll?&y)
{
????if(b1==0){
????????x=1;y=0;return?a1;
????}
????ll?r=ex_gcd(b1,a1%b1,x,y);
????ll?t=x;x=y;
????y=t-a1/b1*y;
????return?r;
}
ll?CRT(int?n)
{
????ll?A=a[1],R=r[1],x,y,temp,d;
????for(int?i=2;i<=n;i++){
????????d=ex_gcd(A,a[i],x,y);
????????if((R-r[i])%d){return?-1;}
????????temp=a[i]/d;
????????x=x*((R-r[i])/d);
????????x=(x%temp+temp)%temp;
????????R-=A*x;
????????A*=temp;
????????R=(R%A+A%A);
????}
????return?R==0?A:(R%A+A)%A;
}
int?main()
{
????int?n;
????while(~scanf("%d",&n)){
????????for(int?i=1;i<=n;i++){
????????????scanf("%lld%lld",&a[i],&r[i]);
????????}
????????printf("%lld\n",CRT(n));
????}
????return?0;
}