// Author: Teoman Ata Korkmaz
#include <bits/stdc++.h>
#define int int64_t
using namespace std;
///////////////////////////////////////////////////////////
int n;
vector<double> a,b;
signed main(void){
cin>>n;
a.resize(n);
b.resize(n);
for(int i=0;i<n;i++)cin>>a[i]>>b[i];
sort(a.rbegin(),a.rend());
sort(b.rbegin(),b.rend());
for(int i=1;i<n;i++)a[i]+=a[i-1];
for(int i=1;i<n;i++)b[i]+=b[i-1];
a.insert(a.begin(),0);
b.insert(b.begin(),0);
// cerr<<fixed<<setprecision(4);
// cerr<<"a:";for(auto i:a)cerr<<" "<<i;cerr<<endl;
// cerr<<"b:";for(auto i:b)cerr<<" "<<i;cerr<<endl;
double ans=0;
int pa=0,pb=0;
while(pa<n && pb<n){
ans=max(ans,min(a[pa],b[pb])-pa-pb);
if(a[pa]<=b[pb])pa++;
else pb++;
}
while(pa<n){
ans=max(ans,min(a[pa],b[pb])-pa-pb);
pa++;
}
while(pb<n){
ans=max(ans,min(a[pa],b[pb])-pa-pb);
pb++;
}
cout<<fixed<<setprecision(4)<<ans<<endl;
}
/*
* min(a[i],b[j])-i-j
*
* insert(x)
* add(x)
* max()
*/
