#include<iostream>
#include<algorithm>
#include<iomanip>
using namespace std;
typedef long long ll;
typedef double db;
const int N = 1e5 + 9;
int n;
db a[N], b[N];
int main() {
cin.tie(NULL)->sync_with_stdio(false);
cin >> n;
for (int i = 1; i <= n; ++i) cin >> a[i] >> b[i];
sort(a + 1, a + n + 1, greater<db>());
sort(b + 1, b + n + 1, greater<db>());
db ans(0), suma(0), sumb(0);
int i(0), j(0);
for (int k = 1; k <= n * 2; ++k) {
if (i != n)
suma += a[++i];
else sumb += b[++j];
while (i && j < n && min(suma, sumb) < min(suma - a[i], sumb + b[j + 1])) {
suma -= a[i--];
sumb += b[++j];
}
while (i < n && j && min(suma, sumb) < min(suma + a[i + 1], sumb - b[j])) {
suma += a[++i];
sumb -= b[j--];
}
ans = max(ans, min(suma, sumb) - k);
}
cout << fixed << setprecision(4) << ans << '\n';
}
/** /\_/\
* (= ._.)
* / >0 \>1
**/
