#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
double n; cin >> n;
vector<double> a(n + 1), b(n + 1), pref(n + 1), prefb(n + 1);
a[0] = 1e9;
b[0] = 1e9;
for (int i = 1; i <= n; i++){
cin >> a[i];
cin >> b[i];
}
sort(a.begin(), a.end());
sort(b.begin(), b.end());
reverse(a.begin(), a.end());
reverse(b.begin(), b.end());
a[0] = 0;
b[0] = 0;
for (int i = 1; i <= n; i++){
pref[i] = pref[i - 1] + a[i];
prefb[i] = prefb[i - 1] + b[i];
}
double ans = 0;
for (double monedas = 0; monedas <= 2 * n; monedas++){
for (int i = 0; i <= min(monedas, n); i++){
int j = monedas - i;
if (0 <= j && j <= n){
ans = max(ans, min(pref[i] - monedas, prefb[j] - monedas));
}
}
}
printf("%.4lf",(double)ans);
}
