#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 100'000 + 10;
int n;
vector<double> a, b;
double ans;
int main() {
cin >> n;
a.resize(n);
b.resize(n);
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
}
sort(a.begin(), a.end(), greater<>());
sort(b.begin(), b.end(), greater<>());
for (int i = 1; i < n; ++i) {
a[i] += a[i - 1];
b[i] += b[i - 1];
}
for (int i = 1; i <= n; ++i) {
int x = int(lower_bound(b.begin(), b.end(), a[i - 1]) - b.begin());
if (x != n) {
ans = max(ans, a[i - 1] - i - 1 - int(lower_bound(b.begin(), b.end(), a[i - 1]) - b.begin()));
}
x = int(lower_bound(a.begin(), a.end(), b[i - 1]) - a.begin());
if (x != n) {
ans = max(ans, b[i - 1] - i - 1 - int(lower_bound(a.begin(), a.end(), b[i - 1]) - a.begin()));
}
}
cout << fixed << setprecision(4) << ans << '\n';
}
