#include <bits/stdc++.h>
using namespace std;
int n;
double ans;
int main()
{
cin.tie(NULL)->sync_with_stdio(false);
cin>>n;
vector<double> a(n), b(n);
for (int i=0; i<n; i++) cin>>a[i]>>b[i];
sort(a.begin(), a.end()); reverse(a.begin(), a.end());
sort(b.begin(), b.end()); reverse(b.begin(), b.end());
for (int i=1; i<n; i++) a[i]+=a[i-1], b[i]+=b[i-1];
for (int i=0; i<n; i++) ans=max(ans, a[i]-(lower_bound(b.begin(), b.end(), a[i])-b.begin())-2-i);
for (int i=0; i<n; i++) ans=max(ans, b[i]-(lower_bound(a.begin(), a.end(), b[i])-a.begin())-2-i);
printf("%.4lf", ans);
}
