#include <cstdio>

#include <cstring>

#include <iostream>

#include <algorithm>

#include <cstdlib>

#include <utility>

#include <vector>

#include <queue>

#include <map>

#include <set>

#define max(x,y) ((x)>(y)?(x):(y))

#define min(x,y) ((x)>(y)?(y):(x))

#define INF 0x3f3f3f3f

#define LL long long

using namespace std;

LL m0, m1, a0, a1;

LL Exgcd(LL a,LL b,LL &x,LL &y) // ax+by = (a,b)

{

    if(b == 0)

    {

        x = 1;

        y = 0;

        return a;

    }

    LL x1,y1,x0,y0;

    x0=1; y0=0;

    x1=0; y1=1;

    x=0; y=1;

    LL r=a%b;

    LL q=(a-r)/b;

    while(r)

    {

        x=x0-q*x1; y=y0-q*y1;

        x0=x1; y0=y1;

        x1=x; y1=y;

        a=b; b=r; r=a%b;

        q=(a-r)/b;

    }

    return b;

}

int main()

{

    int n;

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

    {

        scanf("%lld%lld", &m0, &a0);

        bool flag = 0;

        while(--n)

        {

            scanf("%lld%lld", &m1, &a1);

            LL x, y, tmp;

            LL d = Exgcd(m0, m1, x, y);

            x = (x%(m1/d)+m1/d)%(m1/d);

            tmp = ((a1-a0)%m1+m1)%m1;

            if(tmp%d != 0)

                flag = 1;

            x = x*(tmp/d)%(m1/d);

            a0 = (x*m0+a0+m0/d*m1)%(m0/d*m1);

            m0 = m0/d*m1;

        }

        if(flag)

            printf("-1\n");

        else

            printf("%lld\n", a0);

    }

    return 0;

}