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