#include<iostream>
    #include<cstring>
    #include<cstdio>
    using namespace std;
    typedef long long L;
    int m;
    L a[21],mod[21];
    inline L gcd(L a,L b){
    	return a%b?gcd(b,a%b):b;
    }
    inline L ext_gcd(L a,L b,L &x,L &y){
    	if(b==0){
    		x=1;
    		y=0;
    		return a; 
    	}
    	L gcd(ext_gcd(b,a%b,x,y));
    	L tmp(x);
    	x=y;
    	y=tmp-(a/b)*y;
    	return gcd;
    }
    inline L ny(L a,L b){
    	L x,y;
    	L gcd(ext_gcd(a,b,x,y));
    	if(gcd!=1)
    		return -1;
    	return (x%b+b)%b;
    }
    inline bool merge(L a1,L m1,L a2,L m2,L &a3,L &m3){
    	L d(gcd(m1,m2));
    	L c=a2-a1;
    	if(c%d)
    		return false;
    	c=(c%m2+m2)%m2;
    	m1/=d;
    	m2/=d;
    	c/=d;
    	c*=ny(m1,m2);
    	c%=m2;
    	c*=m1*d;
    	c+=a1;
    	m3=m1*m2*d;
    	a3=(c%m3+m3)%m3;
    	return true;
    }
    L CRT(L a[],L m[],int n){
    	L a1(a[1]),m1(m[1]);
    	for(int i=2;i<=n;i++){
    		L a2(a[i]),m2(m[i]),a3,m3;
    		if(!merge(a1,m1,a2,m2,a3,m3))
    			return -1;
    		a1=a3;
    		m1=m3;
    	}
    	return (a1%m1+m1)%m1;
    }
    inline int gg(){
    	freopen("ccyz.in","r",stdin);
    	freopen("ccyz.out","w",stdout);
    	scanf("%d",&m);
    	for(int i=1;i<=m;i++)
    		scanf("%lld%lld",&mod[i],&a[i]);
    	printf("%lld",CRT(a,mod,m));
    }
    int k(gg());
    int main(){;}