3.03T2

#include<cstdio>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<cstring>
using namespace std;
typedef long long LL;
LL n,a[15],b[15],c[15],m[15];
LL mod = 1,tot1 = 1,tot;
LL gcd(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 -= x * (a / b);
}
int main()
{
    n = read();
    for(int i = 1;i <= n;i++)
    {
        a[i] = read();
        mod *= a[i];
        b[i] = read();
    }
    for(int i = 1;i <= n;i++)
    {
        m[i] = mod / a[i];
        LL x,y;
        gcd(m[i],a[i],x,y);
        x = (x + a[i]) % a[i];
        x *= b[i];
        c[i] = x * m[i];
    }
    LL ans = 0;
    rep(i,1,n) ans += c[i];
    ans %= mod;
    printf("%lld",ans);
    return 0;
}