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

int n;
#define ll long long
const int lim  = 1e6+10;
const double eps = 1e-9;
 
pair<double, int> a[lim];
ll pres[lim], sufs[lim];
double cx(int x){
	return pres[x]/a[x].first;
}
double cy(int y){
	return sufs[y]/(1-a[y].first);
}
int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%lf%d",&a[i].first,&a[i].second);
	}
	sort(a+1,a+n+1,greater<pair<double,int>>());
	int cnt=0;
	for(int i=1;i<=n;i++)
	{
		if(i==1||fabs(a[i].first - a[i - 1].first) > eps)	
			a[++cnt] = a[i];
		else
			a[cnt].second += a[i].second;
	}
	n = cnt;
	for (int i = 1; i <= n; ++i) pres[i] = pres[i - 1] + a[i].second;
    for (int i = n; i; --i) sufs[i] = sufs[i + 1] + a[i].second;
    
    double ans = 0;
    for (int i = 1, p = n; i <= n; ++i) {
		
		while (p > i && cx(i) > cy(p)) --p;
	    ans = max(ans, pres[i] + sufs[p + 1] - cx(i));
	    if (i >= p) break;
	    ans = max(ans, pres[i] + sufs[p] - cy(p));
    }
    cout << fixed << setprecision(10) << ans << '\n';
}