#include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <cstring>
#include <cmath>
#include <map>
#include <unordered_map>
#include <set>
#include <algorithm>
#include <iomanip>
#define F first
#define S second
#define PB push_back
#define PF push_front
#define MP make_pair
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
const int maxn = 1e5 + 10;
const int maxm = 1e5 + 10;
const int mod = 1e9 + 7;
ld p[maxn], q[maxn];
int main() {
ios_base::sync_with_stdio(false);
int n;
cin >> n;
for (int i = 1; i <= n; i++)
cin >> p[i] >> q[i];
sort (p + 1, p + n + 1, greater <ld> ());
sort (q + 1, q + n + 1, greater <ld> ());
ld ans = 0, fi = 0, se = 0;
int idxse = 0;
for (int idxfi = 1; idxfi <= n; idxfi ++) {
fi += p[idxfi] - 1;
se --;
ans = max (ans, min (fi, se));
// cout << idxfi << " " << idxse << " -> " << fi << " " << se << endl;
while (se < fi and idxse < n) {
idxse ++;
se += q[idxse] - 1;
fi --;
// cout << idxfi << " " << idxse << " -> " << fi << " " << se << endl;
ans = max (ans, min (fi, se));
}
}
cout << fixed << setprecision (4) << ans << endl;
}
