#include <iostream>
using namespace std;
int n,a[11],b[11];
long long m = 1;
int mod_n_ni(int a,int b){
    for (int i = 1;i <= b;i++){
        if ((a * i) % b == 1){
            return i;
        }
    }
}
int main(){
    cin >> n;
    for (int i = 0;i < n;i++) {
        cin >> a[i] >> b[i];
        m *= a[i];
    }
    long long ans = 0;
    for (int i = 0;i < n;i++){
        int x = 1;
        for (int j = 0;j < n;j++){
            if (j != i) x *= a[j];
        }
        ans += b[i] * mod_n_ni(x,a[i]) * x;
    }
    while (ans > m) ans -= m;
    cout << ans;
}