#include <bits/stdc++.h>
//#define int long long
#define endl "\n"
using namespace std;

using ll = long long;
const double INF = 1e5;
const int N = 1e6 + 5;

pair<double, ll> a[N];
double p[N];
ll c[N], sc[N];

double getPrice(int l, int r, int n) {
    return sc[l] + sc[n] - sc[r - 1] - max(sc[l] * (1 / (1 - p[l])), (sc[n] - sc[r - 1]) * (1 / p[r]));
}

int main() {
    ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);

    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> a[i].first >> a[i].second;
    }
    sort(a + 1, a + n + 1);
    for (int i = 1; i <= n; i++) {
        p[i] = a[i].first;
        c[i] = a[i].second;
        sc[i] = sc[i - 1] + c[i];
    }

    double ans = -INF;
    for (int l = 1, r = n; l <= n; l++) {
        double x = getPrice(l, r, n);
        while (l < r - 1 && getPrice(l, r - 1, n) >= x) {
            r--;
            x = getPrice(l, r, n);
        }
        ans = max(ans, x);
    }
    cout << fixed << setprecision(20) << ans << endl;

    return 0;
}