/// In The Name Of God
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
#define f first
#define s second
#define pb push_back
#define pp pop_back
#define mp make_pair
#define sz(x) (int)x.size()
#define sqr(x) ((x) * 1ll * (x))
#define all(x) x.begin(), x.end()
#define Kazakhstan ios_base :: sync_with_stdio(0), cin.tie(0), cout.tie(0);
#define nl '\n'
#define ioi exit(0);
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
const int N = (int)5e5 + 7;
const int inf = (int)1e9 + 7;
const int mod = (int)1e9 + 7;
const ll linf = (ll)1e18 + 7;
const ld eps = 1e-4;
const int dx[] = {-1, 0, 1, 0, 1, -1, -1, 1};
const int dy[] = {0, 1, 0, -1, 1, -1, 1, -1};
using namespace std;
int n;
double a[N], b[N];
double s1[N], s2[N];
int main() {
#ifdef IOI2018
freopen ("in.txt", "r", stdin);
//freopen ("B.out", "w", stdout);
#endif
Kazakhstan
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
}
sort(a + 1, a + 1 + n);
sort(b + 1, b + 1 + n);
for (int i = 1; i <= n; i++) {
s1[i] = s1[i - 1] + a[n - i + 1];
s2[i] = s2[i - 1] + b[n - i + 1];
}
double ans = 0;
for (int i = 0; i <= n; i++) {
for (int j = 0; j <= n; j++) {
ans = max(ans, min(s1[i] - i - j, s2[j] - i - j));
}
}
cout << setprecision(4) << fixed << ans;
ioi
}
