#include <algorithm>
#include <iostream>
#include <cmath>
using namespace std;
const int N = 100000;
int aa[N], bb[N];
int main() {
ios_base::sync_with_stdio(false), cin.tie(NULL);
int n; cin >> n;
for (int i = 0; i < n; i++) {
double a, b; cin >> a >> b;
aa[i] = round(a * 10000);
bb[i] = round(b * 10000);
}
sort(aa, aa + n, greater<>());
sort(bb, bb + n, greater<>());
long long ans = 0, s = 0, t = 0;
for (int i = 0, j = 0; i < n || j < n; ) {
if (i < n && (j == n || s < t))
s += aa[i++];
else
t += bb[j++];
ans = max(ans, min(s, t) - (i + j) * 10000);
}
printf("%d.%04d\n", (int) (ans / 10000), (int) (ans % 10000));
return 0;
}
