#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
#define int int64_t
using namespace std;
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
vector<double> as(n);
vector<double> bs(n);
for (int i = 0; i < n; i++) cin >> as[i] >> bs[i];
sort(as.begin(), as.end()); sort(bs.begin(), bs.end());
reverse(as.begin(), as.end()); reverse(bs.begin(), bs.end());
double mx = 0;
double a = 0;
double b = 0;
int ap = 0, bp = 0;
while (ap + bp < 2*n)
{
if (a < b && ap >= n) break;
if (b < a && bp >= n) break;
if (a < b) { a += as[ap]; ap++; }
else { b += bs[bp]; bp++; }
mx = max(mx, min(a, b) - (double)(ap + bp));
}
cout << setprecision(4) << fixed;
cout << mx << "\n";
}
