#include <bits/stdc++.h>
using namespace std;
vector<double> a;
vector<double> b;
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
a.resize(n);
b.resize(n);
for (int i = 0; i<n; i++)cin >> a[i] >> b[i];
sort(a.begin(),a.end(),greater<double>());
sort(b.begin(),b.end(),greater<double>());
int ind=0;
double ans=0,sma=0,smb=0;
for (int i = 0; i<n; i++){
sma+=a[i];
while(ind<n && sma>smb+b[ind])smb+=b[ind++];
ans=max(ans,min(sma,smb)-(double)(i+1+ind));
if (ind<n)smb+=b[ind++];
ans=max(ans,min(sma,smb)-(double)(i+1+ind));
}
cout << fixed << setprecision(4) << ans << '\n';
}
