#include <bits/stdc++.h>
using namespace std;
double solve(vector<double> a, vector<double> b) {
int n = a.size();
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
vector<double> p(n + 1);
for (int i = 0; i < n; i++) {
p[i + 1] = p[i] + b[i];
}
double sum = 0, ans = 0;
for (int i = 0; i < n; i++) {
sum += a[i];
int j = ranges::lower_bound(p, sum) - p.begin();
ans = max(ans, sum - i - j - 1);
}
return ans;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
cin >> n;
vector<double> a(n), b(n);
for (int i = 0; i < n; i++) {
cin >> a[i] >> b[i];
}
cout << fixed << setprecision(4) << max(solve(a, b), solve(b, a)) << '\n';
return 0;
}
