#include <bits/stdc++.h>
using namespace std;
#define int long long
#define all(x) x.begin(), x.end()
#define size(x) (int)x.size()
template<class S, class T>
bool chmin(S &a, const T &b) {
return a > b ? (a = b) == b : false;
}
template<class S, class T>
bool chmax(S &a, const T &b) {
return a < b ? (a = b) == b : false;
}
signed main() {
cin.tie(nullptr)->sync_with_stdio(false);
int n; cin >> n;
vector<double> a(n), b(n);
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
}
sort(all(a)), sort(all(b));
double res = 0;
double A = a.back() - 2, B = b.back() - 2;
a.pop_back(), b.pop_back();
chmax(res, min(A, B));
while (!a.empty() && !b.empty()) {
if (A < B) {
A += a.back() - 1;
B += -1;
a.pop_back();
} else {
B += b.back() - 1;
A += -1;
b.pop_back();
}
chmax(res, min(A, B));
}
while (!a.empty()) {
A += a.back() - 1;
B += -1;
a.pop_back();
chmax(res, min(A, B));
}
while (!b.empty()) {
B += b.back() - 1;
A += -1;
b.pop_back();
chmax(res, min(A, B));
}
cout << fixed << setprecision(4) << res;
}
