#include <bits/stdc++.h>
using namespace std;
#define ll long long
void change(int v, int x, vector<int> &tr) {
v += 1<<18;
tr[v] = x;
while (v > 1) {
v /= 2;
tr[v] = max(tr[v*2], tr[v*2+1]);
}
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
vector<double> a (n, 0), b (n, 0);
for (int i = 0; i < n; i++) {
cin >> a[i] >> b[i];
}
sort(a.begin(), a.end(), greater<double>());
sort(b.begin(), b.end(), greater<double>());
vector<double> pa(n+1, 0), pb (n+1, 0);
set<pair<double, int>> sa, sb;
for (int i = 1; i <= n; i++) {
pa[i] = pa[i-1]+a[i-1];
pb[i] = pb[i-1]+b[i-1];
sa.insert({pa[i], i});
sb.insert({pb[i], i});
}
double sc = 0;
for (int i = 1; i <= n; i++) {
auto x = sb.lower_bound({pa[i], 0});
if (x != sb.end()) {
sc = max(sc, pa[i]-i-(*x).second);
}
auto y = sa.lower_bound({pb[i], 0});
if (y != sa.end()) {
sc = max(sc, pb[i]-i-(*y).second);
}
}
printf("%.4lf",(double)sc);
}
