#include<bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef long long ll;
typedef pair<ll,ll>pll;
const ll INF=0x3f3f3f3f;
const ll MO9=998244353;
const ll MO1=1e9+7;
const ll MO=MO9;
const int N=5e5+5;
ll n,m;
ll s[N];
double p[N];
struct node{
    double p;
    ll c;
}a[N],b[N];
void solve(){
    cin>>n;
    for(int i=1;i<=n;i++)cin>>b[i].p>>b[i].c;
    sort(b+1,b+n+1,[=](node a,node b){
        return a.p>b.p;
    });
    int t=0;
    b[0].p=-1.0;
    for(int i=1;i<=n;i++){
        if(b[i].p==b[i-1].p){
            a[t].c+=b[i].c;
        }
        else a[++t]=b[i];
    }
    n=t;
    for(int i=1;i<=n;i++){
        // cin>>s[i];
        s[i]=a[i].c;
        s[i]+=s[i-1];
        p[i]=a[i].p;
    }
    double ans=0;
    for(int i=1;i<n;i++){
        double tot=1.0*s[i]/p[i];
        // cout<<tot<<' ';
        // cout<<n<<' ';
        // cout<<tot<<'\n';
        int res=n;
        int l=2,r=n;
        while(l<=r){
            int mid=l+r>>1;
            double k=1.0*(s[n]-s[mid-1])/(1.0-p[mid]);
            double ab=s[n]-s[mid-1]+s[i];
            if(k<=tot){
                res=mid;
                ans=max(ans,ab-tot);
                r=mid-1;
            }
            else{
                ans=max(ans,ab-k);
                l=mid+1;
            }
        }

    }
    cout<<fixed<<setprecision(6)<<ans<<'\n';
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);
    int ttt=1;
    // cin>>ttt;
    while(ttt--)
    solve();
    return 0;
}