#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e5 + 5;
int n;
double a[MAXN], b[MAXN];
double solve(int i){
double pa = 0, pb = 0;
int used = 0, inda = 0, indb = 0;
while (pa < i and used < i and inda < n)
pa += a[inda++], used++;
while (pb < i and used < i and indb < n)
pb += b[indb++], used++;
while (used < i and (inda < n or indb < n)){
if (inda < n and pa < pb)
pa += a[inda++];
else
pb += b[indb++];
used++;
}
return min(pa - double(i), pb - double(i));
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
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>());
double res = 0;
int low = 0, high = 2 * n;
while (low < high){
int mid = (low + high) / 2;
double curr = solve(mid);
res = max(res, curr);
if (curr > solve(mid + 1))
high = mid;
else
low = mid + 1;
}
printf("%.4f\n", res);
return 0;
}
