// In the name of God
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define mp make_pair
typedef long long ll;
const int N = 2e5 + 5;
double a[N], b[N], A[N], B[N], mx[N];
int n;
void solve() {
cin >> n;
for (int i = 0; i < n; i++)
cin >> a[i] >> b[i];
sort(a, a + n, greater<double>());
sort(b, b + n, greater<double>());
for (int i = 1; i <= n; i++) {
A[i] = A[i - 1] + a[i - 1] - 1;
B[i] = B[i - 1] + b[i - 1] - 1;
mx[i] = max(mx[i - 1], B[i]);
}
double l = 0, r = 1e9 + 10;
for (int i = 0; i < 120; i++) {
double x = (l + r) / 2.;
bool ok = false;
for (int j = 0; j <= n; j++) {
int r = min((double)n, (A[j] - x));
ok |= r >= 0 && mx[r] >= j + x;
}
if (ok)
l = x;
else
r = x;
}
cout << fixed << setprecision(4) << r << '\n';
}
int32_t main() {
ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
solve();
return 0;
}
