// author:  jieda
// file:	cpp
//#pragma GCC optimize("O3")
#include<bits/stdc++.h>
using namespace std;
# define fi first
# define se second
# define all(x) x.begin(),x.end()
# define stst stringstream
# define pb push_back
# define pf push_front
# define pp push
# define lowbit(x) (x)&(-x)
# define fa(i,op,n) for (int i = op; i <= n; i++)
# define fb(j,op,n) for (ll j = op; j >= n; j--)
# define fg(i,op,n) for (ll i = op; i != n; i = ne[i])
int dx[4] = {-1,0,1,0},dy[4] = {0,1,0,-1};
typedef unsigned long long  ull;
typedef long long ll;
typedef pair<ll,ll> Pll;
typedef pair<int,int> PII;
typedef pair<double,double> PDD;
const int N = 1e5+10,INF = 0x3f3f3f3f,mod = 998244353;
const ll MOD = 212370440130137957ll;//hash(hight)
const int base = 131;
const double eps = 1e-3;
const int seed=10086,mo=1e6+7; //hash(lower)
int prime = 233317;
void solve(){
	int n;cin>>n;
	vector<pair<double,int>> a(n+1);
	fa(i,1,n){
		cin>>a[i].fi>>a[i].se;
	}
	sort(a.begin()+1,a.end(),[&](auto p1,auto p2){
		return p1.fi>p2.fi;
	});
	vector<double> pre(n+2),suf(n+2);
	for(int i = 1;i<=n;i++){
		pre[i] = pre[i-1]+a[i].se;
	}
	for(int i = n;i>=1;i--){
		suf[i] = suf[i+1]+a[i].se;
	}
	double ans = 0;
	for(int i = 1,p = n;i<=n;i++){
		while(p>i&&pre[i]/a[i].fi>suf[p]/(1-a[p].fi)) p--; 
		ans = max(ans,pre[i]+suf[p+1]-pre[i]/a[i].fi);
		if(i>=p) break;
		ans = max(ans,pre[i]+suf[p]-suf[p]/(1-a[p].fi));
	}
	cout<<fixed<<setprecision(10)<<ans<<'\n';
}

int main()
{
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	int t = 1;
	//cin>>t;
	while(t--){
		solve();
	}
	return 0;
}
/*

*/