#include <bits/stdc++.h>
using namespace std;
int main() {
int n;
cin >> n;
vector<double> a(n), b(n);
for (int i = 0; i < n; i++) cin >> a[i] >> b[i];
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
vector<double> sa(n+1, 0), sb(n+1, 0);
for (int i = 0; i < n; i++) {
sa[i+1] = sa[i] + a[i];
sb[i+1] = sb[i] + b[i];
}
double res = 0;
int j = n;
for (int i = 0; i <= n; i++) {
while (j > 0) {
double pa = sa[i] - i - j;
double pb = sb[j] - i - j;
double pa2 = sa[i] - i - (j-1);
double pb2 = sb[j-1] - i - (j-1);
if (min(pa2, pb2) >= min(pa, pb)) j--;
else break;
}
res = max(res, min(sa[i] - i - j, sb[j] - i - j));
}
cout << fixed << setprecision(4) << max(0.0, res) << "\n";
}
