1 //minamoto 2 #include
     
       3 #include
      
        4 #define int long long 5 using namespace std; 6 #define getc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++) 7 char buf[1<<21],*p1=buf,*p2=buf; 8 int read(){ 9     #define num ch-'0'10     char ch;bool flag=0;int res;11     while(!isdigit(ch=getc()))12     (ch=='-')&&(flag=true);13     for(res=num;isdigit(ch=getc());res=res*10+num);14     (flag)&&(res=-res);15     #undef num16     return res;17 }18 const int N=1e5+5;19 int n,ai[N],bi[N];20 int mul(int a,int b,int mod){21     int res=0;22     while(b){23         if(b&1) res=(res+a)%mod;24         a=(a+a)%mod,b>>=1;25     }26     return res;27 }28 int exgcd(int a,int b,int &x,int &y){29     if(b==0) return x=1,y=0,a;30     int gcd=exgcd(b,a%b,x,y),t=x;31     x=y,y=t-a/b*y;return gcd;32 }33 int excrt(){34     int x,y,k,M=bi[1],ans=ai[1];35     for(int i=2;i<=n;++i){36         int a=M,b=bi[i],c=(ai[i]-ans%b+b)%b;37         int gcd=exgcd(a,b,x,y),bg=b/gcd;38         if(c%gcd!=0) return -1;39         x=mul(x,c/gcd,bg);40         ans+=x*M,M*=bg,ans=(ans%M+M)%M;41     }42     return (ans%M+M)%M;43 }44 signed main(){45 //    freopen("testdata.in","r",stdin);46     n=read();47     for(int i=1;i<=n;++i) bi[i]=read(),ai[i]=read();48     printf("%lld\n",excrt());49     return 0;50 }