#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
const int N = 1e5 + 5;
ld a[N], b[N];
int n;
int main() {
cin.tie(0)->sync_with_stdio(0); cout.tie(0);
cin >> n;
for (int i = 1; i <= n; ++i)
cin >> a[i] >> b[i];
sort(a + 1, a + n + 1, greater<ld>());
sort(b + 1, b + n + 1, greater<ld>());
for (int i = 1; i <= n; ++i)
a[i] += a[i - 1], b[i] += b[i - 1];
ld res = 0.0;
for (int i = 1, j = 1; i <= n; ++i) {
while (j <= n && b[j] < a[i]) j++;
if (j <= n) res = max(res, a[i] - i - j);
}
for (int i = 1, j = 1; i <= n; ++i) {
while (j <= n && a[j] < b[i]) j++;
if (j <= n) res = max(res, b[i] - i - j);
}
cout << fixed << setprecision(4) << res;
return 0;
}
