#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;
cin >> n;
vector<double> a(n);
vector<double> b(n);
for (int i = 0; i < n; i++) cin >> a[i] >> b[i];
sort(b.rbegin(), b.rend());
sort(a.rbegin(), a.rend());
//cout << '\n';
double ans = 0;
double ct1 = 0;
for (int i = 0; i < n; i++) {
ct1 += a[i];
double ct2 = 0;
for (int j = 0; j < n; j++) {
double c = i + j + 2;
ct2 += b[j];
//cout << ct1 << ' ' << ct2 << '\n';
ans = max(ans, min(ct1 - c, ct2 - c));
}
}
printf("%.4lf", ans);
return 0;
}
/*
7
*/
