#include <bits/stdc++.h>  
using namespace std;  

#define int long long  

using db = double;

constexpr db eps = 1e-9;

int sgn(db x) {
	if (x > eps) {
		return 1;
	} else if (x < -eps) {
		return -1;
	}
	return 0;	
}

int cmp(db x, db y) {
	return sgn(x - y);
}

signed main() {  
    ios::sync_with_stdio(false);
    cin.tie(nullptr);  

	int n;
	cin >> n;

	vector<db> p_(n + 1), c_(n + 1);
	for (int i = 1; i <= n; i++) {
		cin >> p_[i] >> c_[i];
	}

	vector<int> ord(n + 1);
	iota(ord.begin(), ord.end(), 0);
	sort(ord.begin() + 1, ord.end(), [&](int i, int j) {
		return p_[i] > p_[j];
	});

	vector<db> p(1, -1);
	vector<int>	c(1);
	for (int i = 1; i <= n; i++) {
		if (cmp(p.back(), p_[ord[i]]) == 0) {
			c[c.size() - 1] += c_[ord[i]];
		} else {
			p.push_back(p_[ord[i]]);
			c.push_back(c_[ord[i]]);
		}
	}

	vector<int> suf(n + 2);
	for (int i = n; i >= 1; i--) {
		suf[i] = suf[i + 1] + c[i];
	}

	n = p.size() - 1;
	int sx = 0;
	db ans = -1e18;
	for (int i = 1; i <= n; i++) {
		db x = 1.0 / p[i];
		sx += c[i];
		
		auto calc = [&](int m) {
			db y = 1.0 / (1 - p[m]);
			db sy = suf[m];
			return 1.0 * sx + 1.0 * sy - max(x * sx, y * sy); 
		};

		int l = i, r = n + 1;
		while (r - l > 5) {
			int lm = (2 * l + r) / 3, rm = (l + 2 * r) / 3;
			if (calc(lm) < calc(rm)) {
				l = lm;
			} else {
				r = rm;
			}
		}
		for (int t = l; t <= r; t++) {
			ans = max(ans, calc(t));
		}
	}

	cout << fixed << setprecision(10) << ans << "\n";

    return 0;
}