#include <bits/stdc++.h>
using namespace std;
const int N = 100*1000+5;
pair<double,double> a[N];
double prefa[N],prefb[N];
int main()
{
ios_base::sync_with_stdio(false);
int n;
cin>>n;
for(int i = 1;i<=n;i++) cin>>a[i].first>>a[i].second;
sort(a+1,a+1+n);
reverse(a+1,a+1+n);
for(int i = 1;i<=n;i++) prefa[i] = prefa[i-1]+a[i].first;
for(int i = 1;i<=n;i++) swap(a[i].first,a[i].second);
sort(a+1,a+1+n);
reverse(a+1,a+1+n);
for(int i = 1;i<=n;i++) prefb[i] = prefb[i-1]+a[i].first;
double ans = 0;
for(int i = 0;i<=n;i++){
for(int j = max(0,i-100);j<=min(n,i+100);j++){
ans = max(ans,min(prefa[i],prefb[j])-(i+j));
}
}
printf("%.4lf",(double)ans);
return 0;
}
