#include <bits/stdc++.h>
using namespace std;
const int N = 100005;
int n;
double a[N], b[N];
double sa[N], sb[N];
double ans;
int main()
{
ios_base::sync_with_stdio(false);
cout.setf(ios::fixed);
cout.setf(ios::showpoint);
cout.precision(4);
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)
{
sa[i] = sa[i + 1] + a[i];
sb[i] = sb[i + 1] + b[i];
}
double ans = 0;
for (int i = n; i >= 1; --i)
{
int l = 1, r = n;
while ((r - l) > 3)
{
int m = (l + r) / 2;
if ((sa[i] - (n - i + 1) - (n - m + 1)) <= (sb[m] - (n - i + 1) - (n - m + 1)))
l = m;
else
r = m;
}
for (int m = max(1, l - 5); m <= min(n, r + 5); ++m)
{
ans = max(ans, min((sa[i] - (n - i + 1) - (n - m + 1)), (sb[m] - (n - i + 1) - (n - m + 1))));
}
}
cout << ans << endl;
return 0;
}
