#include "bits/stdc++.h"
using namespace std;
using i64 = long long;
using u64 = unsigned long long;
using i32 = int;
using u32 = unsigned;
using i16 = short;
using u16 = unsigned short;
using ld = long double;
using ii = pair<int, int>;
void solve() {
int n;
cin >> n;
vector<double> a(n), b(n);
for(int i = 0; i < n; ++i) cin >> a[i] >> b[i];
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
int i = 0, j = 0;
double s[2] = {0}, ans = 0;
while(i + j < n + n) {
if(i < n && j < n) {
if(s[0] < s[1]) s[0] += a[i++];
else s[1] += b[j++];
} else if(i < n) s[0] += a[i++];
else s[1] += b[j++];
ans = max(ans, min(s[0], s[1]) - i - j);
}
cout << fixed << setprecision(4) << ans << '\n';
}
int main() {
ios_base :: sync_with_stdio(false);
cin.tie(0);
int t = 1;
//cin >> t;
while(t--) solve();
return 0;
}
