#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned int;
const int N = 1e6+10;
struct tp{
	double p,c;
}a[N];
bool cmp(tp a,tp b){
	return a.p>b.p;
}
double pre[N],suf[N];
signed main() {
    int n;cin>>n;
    for(int i = 1;i<=n;i++){
    	cin>>a[i].p>>a[i].c;
	}
	sort(a+1,a+1+n,cmp);
	for(int i = 1;i<=n;i++){
		pre[i] = pre[i-1] + a[i].c;
	}
	for(int i = n;i>0;i--){
		suf[i] = suf[i+1] + a[i].c;
	}
	double ans = 0;
	double x,y;
	int j = n;
	for(int i = 1;i<=n;i++){
		if(j<=i)break;
		x = 1/a[i].p;
		y = 1/(1-a[j].p);
		double a1 = x * pre[i];
		double a2 = y * suf[j];
		while(a2<a1){
			j--;
			y = 1/(1-a[j].p);
			a2 = y * suf[j];
		}
		if(j<=i){
			j = i+1;
			y = 1/(1-a[j].p);
			ans = max(ans,pre[i] + suf[j] - max(x*pre[i],y*suf[j]));
			break;
			
		}
		ans = max(ans,pre[i] + suf[j] - max(x*pre[i],y*suf[j]));
		y = 1/(1-a[j+1].p);
		ans = max(ans,pre[i] + suf[j+1] - max(x*pre[i],y*suf[j+1]));
		
	}
	cout<<fixed<<setprecision(10)<<ans<<endl;
    
}