#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
#define int long long
int n, a[N], b[N], suma, sumb, res;
long double x, y;
signed main() {
cin.tie(0), cout.tie(0) -> sync_with_stdio(0);
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> x >> y;
a[i] = (int) (x * 10000.0);
b[i] = (int) (y * 10000.0);
}
sort(a + 1, a + n + 1, greater<int>());
sort(b + 1, b + n + 1, greater<int>());
int pa = 0, pb = 0;
for (int i = 1; i <= 2 * n; i++) {
if (suma < sumb && pa < n)
suma += a[++ pa];
else
sumb += b[++ pb];
res = max(res, min(suma, sumb) - i * 10000);
}
cout << fixed << setprecision(4) << (long double) (res / 10000.0);
}
