#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
int n;
long double a[N], b[N];
long double sa[N], sb[N];
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
sa[i] = a[i] - 1;
sb[i] = b[i] - 1;
}
sort(sa + 1, sa + n + 1, greater<long double>());
sort(sb + 1, sb + n + 1, greater<long double>());
long double lo = 0.0F, hi = 1e8;
for (int ite = 1; ite <= 100; ite++) {
long double mid = (lo + hi) * 0.5F;
bool f = false;
long double a = 0, b = 0;
for (int x = 0, y = 0; x <= n; x++) {
while (y + 1 <= n && a - (y + 1) >= mid) {
y++;
b += sb[y];
}
f |= (a - y >= mid && b - x >= mid);
a += sa[x + 1];
}
if (f) {
lo = mid;
} else {
hi = mid;
}
}
cout << fixed << setprecision(4) << lo << '\n';
return 0;
}
