#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);
reverse(a + 1, a + 1 + n);
sort(b + 1, b + 1 + n);
reverse(b + 1, b + 1 + n);
double ans = 0;
int cnt1 = 0, cnt2 = 0;
double sum1 = 0, sum2 = 0;
while (true) {
if (cnt1 >= n and cnt2 >= n) break;
if (cnt1 >= n and cnt2 < n) {
cnt2++;
sum2 += b[cnt2];
}else if(cnt2 >= n and cnt1 < n) {
cnt1++;
sum1 += a[cnt1];
}else if(sum1 <= sum2) {
cnt1++;
sum1 += a[cnt1];
}else{
cnt2++;
sum2 += b[cnt2];
}
ans = max(ans, min(sum1, sum2) - cnt1 - cnt2);
}
cout << fixed << setprecision(4) << ans << endl;
}
