#include <iostream>
#include <algorithm>
using namespace std;

typedef long long LL;
int n;

LL exgcd(LL a, LL b, LL &x, LL &y)
{
    if(!b)
    {
        x = 1, y = 0;
        return a;
    }
    LL d = exgcd(b, a % b, y, x);
    y -= a / b * x;
    return d;
}

int main ()
{
    cin >> n;
    bool flag = true;
    LL a1, m1;
    cin >> a1 >> m1;
    for(int i = 0; i < n - 1; i ++ )
    {
        LL a2, m2;
        cin >> a2 >> m2;
        //先用扩展欧几里得求出k1和k2
        LL k1, k2;
        LL d = exgcd(a1, a2, k1, k2);
        if((m2 - m1) % d)
        {
            flag = false;
            break;
        }
        
        k1 *= (m2 - m1) / d;
        LL t = a2 / d;
        k1 = (k1 % t + t) % t;
        
        m1 = a1 * k1 + m1;
        a1 = abs(a1 / d * a2);
    }
    if(flag)
    {
        cout << (m1 % a1 + a1) % a1;
    }
    else
        cout << "-1" << endl;
    
    return 0;
}

#include<bits/stdc++.h> #define int long long #define abs fabs #define rep(i, a, b) for(int i=a;i<b;++i) #define Rep(i, a, b) for(int i=a;i>=b;--i) using namespace std; const int N = 105; int a[N][N], eps = 1e-8; int n; inline int read(){ int s=0,w=1; char ch=getchar(); while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();} while(ch>='0'&&ch<='9') s=s10+ch-'0',ch=getchar(); return sw; } void put(int x) { if(x<0) putchar('-'),x=-x; if(x>=10) put(x/10); putchar(x%10^48); } int exgcd(int a, int b, int &x, int &y){ if(!b){ x=1, y=0; return a; }else{ int d=exgcd(b, a%b, y, x); y-=a/bx; return d; } } signed main(){ ios::sync_with_stdio(false); cin.tie(0); cout.tie(0); n=read(); int x=0, m1=read(), a1=read(); rep(i, 0, n-1){ int m2=read(), a2=read(); int k1, k2; int d=exgcd(m1, m2, k1, k2); if((a2-a1)%d){ x=-1; break; } k1=(a2-a1)/d; k1=(k1 % (m2/d) + m2/d) % (m2/d); x=k1m1+a1; int m=abs(m1/dm2); a1=k1*m1+a1; m1=m; } if(x!=-1){ x = (a1 % m1 + m1) % m1; } printf("%lld",x); return 0; }