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

//#define ONLINE
#ifndef ONLINE
char DEBUG_BUFFER[1000];
#define debug(...) {sprintf(DEBUG_BUFFER,##__VA_ARGS__);\
cerr<<"\033[1;36m"<<DEBUG_BUFFER<<"\033[0;2m"<<"\033[0m";}
#else
#define debug(...) ;
#endif

using LL=long long;
using PII=pair<int,int>;

#define all(x) (x).begin(),(x).end()
#define allr(x) (x).rbegin(),(x).rend()

#define FAST_IO {ios::sync_with_stdio(false);cin.tie(nullptr);}
inline int read(){static int x; cin>>x; return x;}
inline LL readLL(){static LL x; cin>>x; return x;}
mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());

using LD=long double;
struct node{
	LD p;
	LL c;
};

int main(){
//	freopen("D.in","r",stdin);
//	freopen("D.ans","w",stdout);
	FAST_IO;
	int n=read();
	vector<node>a(n+1);
	for(int i=1;i<=n;i++){
		cin>>a[i].p>>a[i].c;
	}
	sort(a.begin()+1,a.end(),[&](auto& l,auto& r)->bool{
		return l.p>r.p;
	});
	int m=1;
	for(int i=2;i<=n;i++){
		if(a[m].p==a[i].p){
			a[m].c+=a[i].c;
		}
		else{
			a[++m]=a[i];
		}
	}
	vector<LD>x(n+2),y(n+2);
	for(int i=1;i<=m;i++){
		x[i]=x[i-1]+a[i].c;
	}
	for(int i=m;i>0;i--){
		y[i]=y[i+1]+a[i].c;
	}
	vector<LD>ans1(n+2),ans2(n+2);
	for(int i=1;i<=m;i++){
		if(a[i].p==0){
			ans1[i]=1e20;
			continue;
		}
		LD p=1.0/a[i].p;
		ans1[i]=p*x[i];
	}
	for(int i=m;i>0;i--){
		if(a[i].p==1){
			ans2[i]=1e20;
			continue;
		}
		LD p=1.0/(1.0-a[i].p);
		ans2[i]=p*y[i];
	}
	LD ans=0.0;
	for(int i=1;i<=m;i++){
		int l=i+1,r=m+1;
		while(l<r){
			int mid=l+r>>1;
			if(ans2[mid]>ans1[i]){
				l=mid+1;
			}
			else r=mid;
		}
		ans=max(ans,x[i]+y[l]-max(ans1[i],ans2[l]));
		if(l>i+1) l--;
		ans=max(ans,x[i]+y[l]-max(ans1[i],ans2[l]));
	}
	cout<<ans;
	return 0;
}

/* stuff you should look for
* int overflow, array bounds
* special cases (n=1?)
* do smth instead of nothing and stay organized
* WRITE STUFF DOWN
* DON'T GET STUCK ON ONE APPROACH
*/