// Nikoloz Kochashvili
#include <bits/stdc++.h>
using namespace std;
// #define int long long
#define eb emplace_back
#define mp make_pair
#define pb push_back
#define pp pop_back
#define endl '\n'
#define ff first
#define ss second
#define stop exit(0)
#define sz(x) (int)x.size()
#define pause system("pause")
#define all(x) (x).begin(), (x).end()
#define deb(x) cout << #x << "-" << x << endl
typedef char chr;
typedef string str;
typedef long long ll;
typedef vector<int> vii;
typedef pair<int, int> pii;
const long long INF = LLONG_MAX;
const int inf = INT_MAX/2;
const int mod = 998244353;
const int MOD = 1e9 + 7;
const int dx[] = {0, 0, -1, 1};
const int dy[] = {-1, 1, 0, 0};
const double PI = 2 * acos(0.0);
const int N = 2e5 + 5;
int n;
double a[N],b[N];
inline void test_case() {
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 && p2 >= n) break;
if (p1 >= n && p2 < n) {
p2++;
c2 += b[p2];
} else if (p2 >= n && 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 << p1 << " " << p2 << " " << c1 << " " << c2 << endl;
}
printf("%.4lf",(double)ans);
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int T = 1;
// cin >> T;
while (T--) {
test_case();
}
return 0;
}
