#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ios ios::sync_with_stdio(0),cin.tie(0),cout.tie(0)
#define endl '\n'

const int N = 1e6+5;

struct gambler{
	double p;
	ll c;
	bool operator < (gambler &x) const{
		return p>x.p||(p==x.p&&c>x.c);
	} 
}a[N];

ll pre[N];
ll n;
double ans = 0.0;

double calc(int i,int j){
//	if(j<=0||j>n) return -1e15;
	if(a[i].p+1.0-a[j].p<=1.0) return -1e20;
	double x = 1.0/a[i].p;
	double sx = 1.0*pre[i];
	double y = 1.0/(1.0-a[j].p);
	double sy = 1.0*(pre[n]-pre[j-1]);
	double t = (sx+sy-1.0*max(sx*x,sy*y));
	ans = max(ans,t);
	return t;
}

void solve(){
	cin>>n;
	for(int i=1;i<=n;i++) cin>>a[i].p>>a[i].c;
	sort(a+1,a+1+n);
	pre[0] = 0;
	for(int i=1;i<=n;i++) pre[i] = pre[i-1]+a[i].c;
	//double ans = 0.0;
	for(int i=1;i<=n-1;i++){
		ll l = 1, r = n;
		double anst = max(calc(i,l),calc(i,r));
		while(l<=r){
			int lmid = l+(r-l)/3;
			int rmid = r-(r-l)/3;
			//cout<<lmid<<' '<<calc(i,lmid)<<endl;
			//cout<<rmid<<' '<<calc(i,rmid)<<endl;
			if(calc(i,lmid) <= calc(i,rmid)) l = lmid+1;
			else r = rmid-1;
		}
		anst = max(calc(i,l),calc(i,r));
		ans = max(ans,anst);
		//cout<<anst<<endl;
	}
	//cout<<calc(1,3)<<endl;
	cout<<fixed<<setprecision(10)<<ans<<endl;
} 

int main(){
	ios;
	//ll T;cin>>T;while(T--)
	solve();
	return 0;
}