#include <bits/stdc++.h>

using namespace std;
using ll = long long;

const int inf = 2e9 + 7;
const double eps = 1e-8;

void solve() {
    int n;
    cin >> n;
    vector<pair<double, int> > a(n);
    for (auto &[p, c] : a) {
        cin >> p >> c;
    }
    sort(a.begin(), a.end());
    reverse(a.begin(), a.end());
    vector<pair<double, int> > b;
    for (int i = 0; i < n; ) {
        b.push_back(a[i]);
        i++;
        while (i < n && b.back().first == a[i].first) {
            b.back().second += a[i].second;
            i++;
        }
    }
    swap(a, b);
    n = a.size();
    ll sum1 = 0, sum2 = 0;
    double ans = 0;
    double y = 0;
    for (int i = 0, j = n - 1; i < n; ++i) {
        double x = 1 / a[i].first;
        sum1 += a[i].second;
        while (i < j && a[j].first != 1 && (1 / (1 - a[j].first) * (sum2 + a[j].second) <= sum1 * x || fabs(1 / (1 - a[j].first) * (sum2 + a[j].second) - sum1 * x) < eps)) {
            sum2 += a[j].second;
            y = 1 / (1 - a[j].first);
            j--;
        }
        // if (y != 0) {
            ans = max(ans, sum1 + sum2 - max(sum1 * x, sum2 * y));
        // }
        if (i < j) {
            double z = 1 / (1 - a[j].first);
            ans = max(ans, sum1 + sum2 + a[j].second - max(sum1 * x, (sum2 + a[j].second) * z));
        } else {
            break;
        }
    }
    cout << fixed << setprecision(12) << ans << "\n";
}

int main(void) {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}