#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 17;
long double ans, a[N], b[N], fa[N], fb[N];
int n, z;
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> n;
for (int i = 1; i <= n; i++) cin >> a[i] >> b[i];
sort (a + 1, a + n + 1);
sort (b + 1, b + n + 1);
for (int i = n; i >= 1; i--)
{
fa[n - i + 1] = fa[n - i] + a[i];
fb[n - i + 1] = fb[n - i] + b[i];
}
for (int i = 1; i <= n; i++)
{
z = lower_bound (fb + 1, fb + n + 1, fa[i]) - fb;
if (z <= n)
{
ans = max (ans, fa[i] - i - z);
}
z = lower_bound (fa + 1, fa + n + 1, fb[i]) - fa;
if (z <= n)
{
ans = max (ans, fb[i] - i - z);
}
}
printf("%.4lf",(double) ans);
}
