#include "bits/stdc++.h"
using namespace std;
#define ar array
typedef int64_t ll;
signed main(){
ios::sync_with_stdio(0); cin.tie(0);
int n; cin>>n;
vector<double> a(n), b(n);
for(int i=0;i<n;i++){
cin>>a[i]>>b[i];
}
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
a.insert(a.begin(), 0);
b.insert(b.begin(), 0);
for(int i=1;i<=n;i++){
a[i] += a[i-1];
}
for(int i=1;i<=n;i++){
b[i] += b[i-1];
}
//~ for(int i=1;i<=n;i++){
//~ cout<<a[i]<<" ";
//~ } cout<<"\n";
//~ for(int i=1;i<=n;i++){
//~ cout<<b[i]<<" ";
//~ } cout<<"\n";
double res = -1e9;
for(int i=0;i<=n;i++){
int j = lower_bound(b.begin(), b.end(), a[i]) - b.begin();
if(j <= n && a[i] <= b[j]){
res = max(res, a[i] - i - j);
}
}
for(int i=0;i<=n;i++){
int j = lower_bound(a.begin(), a.end(), b[i]) - a.begin();
if(j <= n && b[i] <= a[j]){
res = max(res, b[i] - i - j);
}
}
//~ for(int i=0;i<=n;i++){
//~ for(int j=0;j<=n;j++){
//~ res = max(res, min(a[i], b[j]) - i - j);
//~ }
//~ }
//~ printf("%.4lf",(double)res);
cout<<fixed<<setprecision(4)<<res<<"\n";
}
