#include "bits/stdc++.h"
using namespace std;
/*
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using ordered_set = tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>;
*/
#define all(x) begin(x), end(x)
#define sz(x) (int)x.size()
using ll = long long;
const int mod = 1e9+7;
void solve(int tc) {
int n;
cin >> n;
vector<double> a(n+1), b(n+1);
for (int i = 0; i < n; ++i) cin >> a[i] >> b[i];
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
int i = 0, j = 0;
double ans = 0, suma = 0, sumb = 0;
while (i <= n and j <= n) {
if (suma > sumb) {
sumb += b[j];
++j;
} else {
suma += a[i];
++i;
}
ans = max(ans, min(suma, sumb) - i - j);
// cerr << "ans, suma, sumb : " << ans << " " << suma << " " << sumb << '\n';
}
cout << fixed << setprecision(4) << ans << '\n';
}
signed main() {
ios_base::sync_with_stdio(false); cin.tie(NULL);
int tc = 1;
//cin >> tc;
for (int i = 1; i <= tc; ++i) solve(i);
return 0;
}
