#include <iostream>
#include <vector>
#include <utility>
#include <algorithm>
#include <iomanip>
const double EPS = 1e-9;
int main(){
int n;
std::cin >> n;
std::vector<double> a = {0.0}, b = {0.0};
for(int i = 0; i < n; i++){
double x, y;
std::cin >> x >> y;
a.push_back(x - 1.0);
b.push_back(y - 1.0);
}
sort(a.rbegin(), a.rend() - 1);
sort(b.rbegin(), b.rend() - 1);
for(int i = 1; i <= n; ++i) {
a[i] += a[i - 1];
b[i] += b[i - 1];
}
double ans = 0.0;
for(int k = 0; k < 2; ++k) {
for(int i = 0; i <= n; ++i) {
int lo = 1, hi = std::min(n, static_cast<int>(a[i])), best_j = 0;
while(lo <= hi) {
int j = (lo + hi) / 2;
if( a[i] - j <= b[j] - i + EPS ) {
hi = j - 1;
best_j = j;
} else {
lo = j + 1;
}
}
ans = std::max(ans, std::min(a[i] - best_j, b[best_j] - i));
}
swap(a, b);
}
std::cout << std::fixed << std::setprecision(4) << ans << std::endl;
return 0;
}
