#include <iostream>

#include <cstdio>

#include <cstring>

#include <algorithm>

#include <cmath>

using namespace std;

typedef long long ll;

inline ll read(){

    char c=getchar();ll x=,f=;

    while(c<''||c>''){if(c=='-')f=-;c=getchar();}

    while(c>=''&&c<=''){x=x*+c-'';c=getchar();}

    return x*f;

}

ll n,a1,m1,a2,m2;

void exgcd(ll a,ll b,ll &d,ll &x,ll &y){

    if(b==) d=a,x=,y=;

    else exgcd(b,a%b,d,y,x),y-=(a/b)*x;

}

int main(){

    freopen("in","r",stdin);

    while(scanf("%lld",&n)!=EOF){

        int flag=;

        m1=read();a1=read();n--;

        while(n--){

            m2=read();a2=read();

            if(flag) continue;

            ll d,t1,t2;

            exgcd(m1,m2,d,t1,t2);

            if((a2-a1)%d){flag=;continue;}

            t1*=(a2-a1)/d;

            m2/=d;

            t1=(t1%m2+m2)%m2;

            a1=a1+m1*t1;

            m1*=m2;

        }

        if(flag) puts("-1");

        else printf("%lld\n",a1);

    }

}