#include <bits/stdc++.h>
using namespace std;
#define all(a) a.begin(), a.end()
int main()
{
    int n;
    cin >> n;
    vector<pair<double, int>> a(n);
    int sum = 0;
    int cntx = 0;
    int cnty = 0;
    for (int i = 0; i < n; i++)
    {
        cin >> a[i].first >> a[i].second;
        sum += a[i].second;
    }
    a.emplace_back(1, 0);
    a.emplace_back(0, 0);
    sort(all(a), greater());
    double ans = 0;
    int r = n + 1;
    double sy = 0;
    for (int i = 0; a[i].first > 0; i++)
    {
        cntx += a[i].second;
        double x = 1 / a[i].first;
        double sx = x * cntx;
        while (sy <= sx && a[r].first < 1)
        {
            ans = max(ans, cnty + cntx - sx);
            cnty += a[r].second;
            double y = 1 / (1 - a[r].first);
            sy = y * cnty;
            r--;
        }
        ans = max(ans, cnty + cntx - max(sx, sy));
    }
    cout << fixed << setprecision(12) << ans << "\n";
    return 0;
}