#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100005;
long long n, m = 1, ans = 0;
long long a[MAXN], b[MAXN];

long long exgcd (long long r1, long long r2, long long &x, long long &y) {
    if (r2 == 0) { x = 1, y = 0; return r1; }
    long long r3 = exgcd (r2, r1 % r2, x, y);
    long long z = x; x = y; y = z - y * (r1 / r2);
    return r3;
}

long long solve (long long r1, long long r2, long long mod) {
    long long x0, y0, gc;
    gc = exgcd (r1, mod, x0, y0); x0 = x0 * r2 / gc;
    return x0;
}

int main () {
    freopen ("ccyz.in", "r", stdin);
    freopen ("ccyz.out", "w", stdout);
    cin >> n;
    for (int q = 1; q <= n; ++q) {
        cin >> b[q] >> a[q]; m *= b[q];
    }
    for (int q = 1; q <= n; ++q) {
        ans += a[q] * (m / b[q]) * solve (m / b[q], 1, b[q]); ans %= m;
    }
    cout << ans << endl;
    return 0;
}