#include <bits/stdc++.h>
using namespace std;
using namespace chrono;
#define ll long long
#define ld long double
#define all(a) (a).begin(), (a).end()
#define allr(a) (a).rbegin(), (a).rend()
#define pb push_back
#define S second
#define F first
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define INF (ll)1e18
#define int ll
#define pld pair<ld,ld>
void solve() {
int n; cin >> n;
vector<ld> a(n),b(n);
for (int i= 0; i < n; i++){
cin >> a[i] >> b[i];
}
sort(allr(a));
sort(allr(b));
ld ans = 0;
int p1 = 1, p2 = 1;
ld cur = a[0] + b[0];
ld Aw = a[0], Bw = b[0];
ld cost = 2;
ans = min(Aw - cost, Bw - cost);
while(p1 < n && p2 < n){
while(p1 < n && Aw < Bw){
Aw += a[p1++]; cost++;
ans = max(ans, min(Aw - cost, Bw - cost));
}
while(p2 < n && Bw <= Aw){
Bw += b[p2++]; cost++;
ans = max(ans, min(Aw - cost, Bw - cost));
}
}
cout << ans << '\n';
}
signed main() {
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cout << fixed << setprecision(4);
int t = 1;
//cin >> t;
while (t--)
solve();
return 0;
}
