#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
const int N = 1e5 + 10;
double a[N], b[N];
int main(int argc, char const *argv[]) {
#ifdef LOCAL_TESTING
freopen("in", "r", stdin);
#endif
int n; cin >> n;
for(int i = 1; i <= n; i++)
cin >> a[i] >> b[i];
sort(a + 1, a + n + 1, greater<double>());
sort(b + 1, b + n + 1, greater<double>());
for(int i = 1; i <= n; i++)
a[i] += a[i - 1], b[i] += b[i - 1];
double ans = 0;
for(int i = 0; i <= n; i++) {
int lo = 0, hi = n;
while(lo <= hi) {
int m1 = lo + (hi - lo) / 3;
int m2 = hi - (hi - lo) / 3;
double f1 = min(a[i], b[m1]) - i - m1;
double f2 = min(a[i], b[m2]) - i - m2;
ans = max({ans, f1, f2});
if(f1 < f2) lo = m1 + 1;
else hi = m2 - 1;
}
}
cout << fixed << setprecision(4) << ans << endl;
}
