#include <bits/stdc++.h>
using namespace std;
void setup()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
}
int n, l, r, m;
double a[100001], b[100001], res;
int main()
{
setup();
cin >> n;
for (int i = 1; i <= n; ++i)
{
cin >> a[i] >> b[i];
a[i] -= 1;
b[i] -= 1;
}
sort(a + 1, a + 1 + n, greater<double>());
sort(b + 1, b + 1 + n, greater<double>());
for (int i = 1; i <= n; ++i)
{
a[i] += a[i - 1];
b[i] += b[i - 1];
}
for (int i = 1; i <= n; ++i)
{
l = 1;
r = n;
while (l <= r)
{
m = (l + r) >> 1;
res = max(res, min(a[i] - m, b[m] - i));
if (a[i] - m > b[m] - i)
{
l = m + 1;
}
else
{
r = m - 1;
}
}
}
cout << fixed << setprecision(4) << res;
return 0;
}
