#include <bits/stdc++.h>

using namespace std;

#define dbg(x) cerr << #x << "=" << x << "\n"
#define MULTI int _; cin >> _; while (_--)

#define int long long
#define double long double
#define ull unsigned long long
typedef long long ll;

const int N = 1e6 + 5, INF = 0x3f3f3f3f3f3f3f3f;

struct Node {
	double p;
	int c;
	
	bool operator<(const Node &x) const {
		return p > x.p;
	}
};

void solve() {
	int n;
	cin >> n;
	
	vector<Node> a;
	map<double, int> mp;
	
	for (int i = 0; i < n; i++) {
		double p;
		int c;
		cin >> p >> c;
		mp[p] += c;
	}
	for (auto it : mp) {
		a.push_back({it.first, it.second});
	}
	
	n = a.size();
	
	sort(a.begin(), a.end());
	
	vector<int> sy(n + 1);
	int sx = 0;
	for (int i = n - 1; i >= 0; i--) {
		sy[i] = sy[i + 1] + a[i].c;
	}
	
	double res = 0;
	for (int i = 0; i < n; i++) {
		double x = 1.0 / a[i].p;
		sx += a[i].c;
		
		int l = i + 1, r = n, lm, rm;
		double ans = -INF;
		while (l < r) {
			lm = l + (r - l) / 3;
			rm = r - (r - l) / 3;
			
			function<double(int)> check = [&](int mid) -> double {
				if (mid == n) {
					return sx - sx * x;
				}
				return sx + sy[mid] - max(sx * x, sy[mid] * 1.0 / (1.0 - a[mid].p));
			};
			
			double ck1 = check(lm), ck2 = check(rm);
			if (ck1 < ck2) {
				ans = max(ans, ck2);
				r = rm - 1;
			} else {
				ans = max(ans, ck1);
				l = lm + 1;
			}
		}
		
		res = max(res, ans);
	}
	
	cout << fixed << setprecision(10);
	cout << res << "\n";
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	solve();
	return 0;
}