#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;
const int N=10+5;
int n;
ull a[N],b[N],m=1;
ull ans=0;
ull fst(ull x,ull y,ull mod){
    if (y==0)return 1;
    if (y%2==1)return fst(x,y-1,mod)%mod*x%mod;
    ull p=fst(x,y/2,mod)%mod;
    return p*p%mod;
}
int main(){
    freopen ("ccyz.in","r",stdin);
    freopen ("ccyz.out","w",stdout);
    scanf("%d",&n);
    for (int i=1;i<=n;i++){
        scanf("%llu%llu",&a[i],&b[i]);
        m*=a[i];
    }
    for (int i=1;i<=n;i++){
        ull t=m/a[i];
        ans=(ans+b[i]%m*fst(t,a[i]-2,a[i])%m*t%m)%m;
    }
    printf("%llu\n",ans);
    return 0;
}