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

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define pb push_back
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vi;

int main() {
	cin.tie(0)->sync_with_stdio(0);
	int n;
    cin >> n;
	vector<ll> p(n), w(n);
	ll torque = 0;
	for(int i = 0; i < n; i++) {
		cin >> p[i] >> w[i];
		torque += p[i]*w[i];
	}
	if(torque > 0) {
		torque = -torque;
		for(int i = 0; i < n; i++)
			p[i] = -p[i];
		reverse(all(p));
		reverse(all(w));
	}

	struct Group {
		ll W = 0, N = 0, pos = 0, id = 0;
		bool operator<(const Group g) const {
			if(W*g.N == g.W*N)
			    return id < g.id;
			return W*g.N < g.W*N;
		}
	};

	set<pair<ll, Group>> positions;
	vector<bool> killed(n);
	priority_queue<Group> q;
	for(int i = 0; i < n; i++) {
	    Group g{w[i], 1, p[i], i};
		q.push(g);
	    positions.insert({p[i], g});
	}
	ld ans = 0;
	ld T = -torque;
	while(T > 0) {
		while(killed[q.top().id])
			q.pop();
		Group curr = q.top();
		q.pop();
		auto next = positions.upper_bound({curr.pos, curr});
		if(next != positions.end()) {
			ll dist = next->second.pos-curr.pos;
			if(dist*curr.W < T) {
				ans += dist*curr.N;
				T -= dist*curr.W;

				positions.erase(positions.find({curr.pos, curr}));
				curr.pos = next->second.pos;
				curr.W += next->second.W;
				curr.N += next->second.N;
				positions.insert({curr.pos, curr});
				q.push(curr);
				
				killed[next->second.id] = true;
			    positions.erase(next);
			}
			else {
				ans += (ld)T/curr.W*curr.N;
				T = 0;
			}
		}
		else {
			ans += (ld)T/curr.W*curr.N;
			T = 0;
		}
	}
	cout << fixed << setprecision(10) << ans << "\n";
}