#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);
for (int i = 0; i <= n; ++i) {
suma += a[i];
sumb = 0;
for (int j = 0; j <= n; ++j) {
sumb += b[j];
ans = max(ans, min(suma, sumb) - i - j);
}
}
cout << fixed << setprecision(4) << ans << '\n';
}
/** /\_/\
* (= ._.)
* / >0 \>1
**/
