#include <iostream>
#include <vector>
#include <random>
#include <algorithm>
#include <cassert>
#include <cstring>
#include <iomanip>
using namespace std;
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int n;
cin >> n;
vector<double> a(n);
vector<double> b(n);
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
}
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
vector<double> pa(n + 1, 0);
vector<double> pb(n + 1, 0);
for (int i = 1; i <= n; ++i) {
pa[i] = pa[i - 1] + a[i - 1];
pb[i] = pb[i - 1] + b[i - 1];
}
auto slv = [&] (vector<double> pa, vector<double> pb) {
double ans = 0;
for (int i = 0; i <= n; ++i) {
if (pb.back() < pa[i]) break;
int j = lower_bound(pb.begin(), pb.end(), pa[i]) - pb.begin();
ans = max(ans, pa[i] - i - j);
}
return ans;
};
cout << fixed << setprecision(4) << max(slv(pa, pb), slv(pb, pa));
}
