#include <bits/stdc++.h>
#define fi first
#define se second
#define mp make_pair
#define all(x) x.begin(), x.end()
using namespace std;
template <class X, class Y> bool minimize(X &a, Y b) {
if (a > b) return a = b, true;
return false;
}
template <class X, class Y> bool maximize(X &a, Y b) {
if (a < b) return a = b, true;
return false;
}
const int N = 1e5 + 7;
int n;
double a[N];
double b[N];
double pre_a[N];
double pre_b[N];
double res;
signed main() {
cin.tie(0)->sync_with_stdio(0);
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);
reverse(a + 1, a + n + 1);
reverse(b + 1, b + n + 1);
for (int i = 1; i <= n; i ++) {
pre_a[i] = pre_a[i - 1] + a[i];
pre_b[i] = pre_b[i - 1] + b[i];
}
for (int i = 1, j = 1; i <= n; i ++) {
while (j < n && pre_a[j + 1] <= pre_b[i]) {
j ++;
}
if (pre_b[i] < pre_a[j]) {
maximize(res, pre_b[i] - i - j);
} else {
maximize(res, pre_a[j] - i - j);
if (j < n) maximize(res, pre_b[i] - i - j - 1);
}
}
cout << fixed << setprecision(4) << res;
return 0;
}
