#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF (int)1e18
#define f first
#define s second
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
void Solve()
{
int n; 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(), greater<double>());
sort(b.begin(), b.end(), greater<double>());
vector <double> pa, pb;
pa.push_back(0);
pb.push_back(0);
for (auto x : a) pa.push_back(pa.back() + x);
for (auto x : b) pb.push_back(pb.back() + x);
double ans = 0;
for (int i = 0; i <= n; i++){
int id = lower_bound(pb.begin(), pb.end(), pa[i]) - pb.begin();
if (id > n) continue;
ans = max(ans, pa[i] - i - id);
}
for (int i = 0; i <= n; i++){
int id = lower_bound(pa.begin(), pa.end(), pb[i]) - pa.begin();
if (id > n) continue;
ans = max(ans, pb[i] - i - id);
}
cout << fixed << setprecision(4) << ans << "\n";
}
int32_t main()
{
auto begin = std::chrono::high_resolution_clock::now();
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
// cin >> t;
for(int i = 1; i <= t; i++)
{
//cout << "Case #" << i << ": ";
Solve();
}
auto end = std::chrono::high_resolution_clock::now();
auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n";
return 0;
}
