#include <bits/stdc++.h>
using namespace std;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n; cin >> n;
vector<long long> a(n), b(n);
for (int i = 0; i < n; i++){
long double x, y; cin >> x >> y;
x *= 10000; y *= 10000;
a[i] = (long long)x; b[i] = (long long)y;
}
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
long long ans = 0, sa = 0, sb = 0, ptr_a = 0, ptr_b = 0;
for (long long i = 1; i <= 2 * n; i++){
if (sa < sb && ptr_a != n){
sa += a[ptr_a];
ptr_a++;
}
else{
sb += b[ptr_b];
ptr_b++;
}
ans = max(ans, min(sa, sb) - i * 10000);
}
printf("%.4lf\n", (ans + 0.0) / 10000);
}
