#include <bits/stdc++.h>
#define int long long
#define pb push_back
#define fs first
#define sc second
using namespace std;
const int N = 100005;
double a[N], b[N];
int n;
signed main() {
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
}
sort(a + 1, a + 1 + n, greater<double>());
sort(b + 1, b + 1 + n, greater<double>());
double ans = 0;
int p1 = 0; int p2 = 0;
double c1 = 0, c2 = 0;
while (true) {
if (p1 >= n and p2 >= n) break;
if (p1 >= n and p2 < n) {
p2++;
c2 += b[p2];
}else if(p2 >= n and p1 < n) {
p1++;
c1 += a[p1];
}else if(c1 <= c2) {
p1++;
c1 += a[p1];
}else{
p2++;
c2 += b[p2];
}
ans = max(ans, min(c1, c2) - p1 - p2);
}
cout << fixed << setprecision(4) << ans << endl;
}
