#include <bits/stdc++.h>
using namespace std;
#define int long long
signed 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> pa(n + 1, 0.0);
vector<double> pb(n + 1, 0.0);
for (int i = 1; i <= n; i++) {
pa[i] = pa[i - 1] + a[i - 1];
pb[i] = pb[i - 1] + b[i - 1];
}
double ans = 0.0;
int y = 0;
for (int x = 0; x <= n; x++) {
while (y < n and pb[y + 1] <= pa[x]) {
y++;
}
ans = max(ans, min(pa[x], pb[y]) - x - y);
if (y + 1 <= n) {
ans = max(ans, min(pa[x], pb[y + 1]) - x - y - 1);
}
}
cout << fixed << setprecision(9) << ans << endl;
return 0;
}
