#include <bits/stdc++.h>
using i64 = long long;
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
cin >> n;
vector<double> a(n), b(n);
for (int i = 0; i < n; i++) {
cin >> a[i] >> b[i];
}
sort(a.begin(), a.end(), greater());
sort(b.begin(), b.end(), greater());
vector<double> pa(n + 1), pb(n + 1);
for (int i = 0; i < n; i++) {
pa[i + 1] = pa[i] + a[i];
pb[i + 1] = pb[i] + b[i];
}
double ans = 0;
for (int i = 1, j = 0; i <= n; i++) {
while (j < n && pb[j] < pa[i]) {
j++;
}
ans = max(ans, min(pa[i], pb[j]) - i - j);
}
for (int i = 1, j = 0; i <= n; i++) {
while (j < n && pa[j] < pb[i]) {
j++;
}
ans = max(ans, min(pa[j], pb[i]) - i - j);
}
cout << fixed << setprecision(4);
cout << ans << "\n";
return 0;
}
