1 #include<cstdio>
 2 #define ll long long
 3 
 4 ll a,b,c;
 5 ll x,y;
 6 
 7 ll r[1010],m[1010];
 8 
 9 void exgcd(ll a,ll b,ll& d,ll &x, ll &y)
10 {
11    if(!b)
12    {
13        d=a;
14        x=1;
15        y=0;
16    }
17    else
18    {
19        exgcd(b,a%b,d,y,x);
20        y-=x*(a/b);
21    }
22 }
23 
24 ll crt(ll m[],ll r[],int n)
25 {
26     ll M=m[1],R=r[1],x,y,d;
27     for(int i=2;i<=n;i++)
28     {
29         exgcd(M,m[i],d,x,y);
30         if( (r[i]-R)%d ) return -1;
31         x=(r[i]-R)/d*x%(m[i]/d);
32         R+=M*x;
33         M=M*m[i]/d;
34         R%=M;
35     }
36     return R>0?R:R+M;
37 }
38 
39 int main()
40 {
41     int n;
42     while(scanf("%d",&n)!=EOF)
43     {
44         for(int i=1;i<=n;i++)
45         {
46             scanf("%lld%lld",&m[i],&r[i]);
47         }
48         ll ans=crt(m,r,n);
49        printf("%lld\n",ans);
50     }
51 
52 }