#include <bits/stdc++.h>
using namespace std;
#define forsn(i, s, n) for (int i = int(s); i < int(n); i++)
#define forn(i, n) forsn(i, 0, n)
#define dforsn(i, s, n) for (int i = int(n) - 1; i >= int(s); i--)
#define dforn(i, n) dforsn(i, 0, n)
#define foreach(it, c) for (auto it = begin(c); it != end(c); it++)
#define sz(x) int(x.size())
#define all(x) begin(x), end(x)
#define pb push_back
#define eb emplace_back
using vi = vector<int>;
using ll = long long;
using ld = long double;
using vll = vector<ll>;
using ii = pair<int, int>;
#define fst first
#define snd second
const ll INF = 1e18;
int main() {
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int n;
cin >> n;
vector<ld> a(n), b(n);
forn(i, n) cin >> a[i] >> b[i];
sort(all(a), greater<ld>());
sort(all(b), greater<ld>());
vector<ld> prefA(n + 1), prefB(n + 1);
forn(i, n) prefA[i + 1] = prefA[i] + a[i];
forn(i, n) prefB[i + 1] = prefB[i] + b[i];
ld ret = 0.0;
forsn(s, 1, 2 * n + 1) {
int lo = max(0, s - n) - 1, hi = min(n, s);
auto f = [&](int i) {
assert(0 <= i && i <= n);
assert(0 <= s - i && s - i <= n);
return min(prefA[i], prefB[s - i]);
};
while (hi - lo > 1) {
int mid = (lo + hi) / 2;
if (f(mid) < f(mid + 1)) {
lo = mid;
} else {
hi = mid;
}
}
ret = max(ret, f(hi) - s);
}
cout << fixed << setprecision(4) << ret << '\n';
return 0;
}
