#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 longusing 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;}