#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
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> pa(n+1, 0), pb(n+1, 0);
for (int i = 1; i <= n; i++) {
pa[i] = pa[i-1] + a[i-1];
pb[i] = pb[i-1] + b[i-1];
}
double res = 0;
for (int i = 0; i <= n; i++) {
int j1 = lower_bound(pb.begin(), pb.end(), pa[i]) - pb.begin();
for (int d = -1; d <= 0; d++) {
int j = j1 + d;
if (j < 0 || j > n) continue;
double val = min(pa[i], pb[j]) - (i + j);
res = max(res, val);
}
}
cout << fixed << setprecision(4) << max(0.0, res) << '\n';
}
