//Oh? You're Approaching Me?
#include <bits/stdc++.h>
//#include <fstream>
using namespace std;
//
#define int long long
typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
// #pragma GCC optimize("O3,unroll-loops")
#define migmig ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define pb push_back
#define F first
#define S second
#define SZ(x) ll((x).size())
#define all(x) (x).begin(), (x).end()
#define cl clear
#define endl '\n'
#define deb(x) cerr << #x << " = " << x << '\n'
#define dokme(x) {cout << x << endl; return;}
#define wtf cout << "[ahaaaaaaaaaaaaaaaa]" << endl;
const int maxn = 2e5 + 100;
const int mod = 998244353;
const int inf = 1e18 + 5;
const int LOG = 61;
#define mid ((l + r) / 2)
#define lc (id * 2)
#define rc (lc + 1)
//g++ main.cpp -o main && main.exe
int n;
double a[maxn], b[maxn];
signed main() {
migmig;
cin >> n;
for (int i = 0; i < n; i++)
cin >> a[i] >> b[i];
sort(a, a + n);
sort(b, b + n);
reverse(a, a + n);
reverse(b, b + n);
int pa = 0, pb = 0;
double ans = 0, sa = 0, sb = 0;
while (pa < n && pb < n) {
if (sa < sb) {
sa += a[pa];
pa++;
}
else {
sb += b[pb];
pb++;
}
ans = max(ans, min(sa, sb) - pa - pb);
}
while (pa < n) {
sa += a[pa];
pa++;
ans = max(ans, min(sa, sb) - pa - pb);
}
while (pb < n) {
sb += b[pb];
pb++;
ans = max(ans, min(sa, sb) - pa - pb);
}
cout << fixed << setprecision(11) << ans << '\n';
}
