/**
* author: Haunted_Cpp
**/
#include <bits/stdc++.h>
using namespace std;
#pragma GCC target("fma,sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#pragma GCC optimize("unroll-loops")
template<typename T> ostream &operator << (ostream &os, const vector<T> &v) { os << '{'; string sep; for (const auto &x : v) os << sep << x, sep = ", "; return os << '}'; }
template<typename T, size_t size> ostream &operator << (ostream &os, const array<T, size> &arr) { os << '{'; string sep; for (const auto &x : arr) os << sep << x, sep = ", "; return os << '}'; }
template<typename A, typename B> ostream &operator << (ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
void debug_out() { cerr << endl; }
template<typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cerr << ' ' << H; debug_out(T...); }
#ifdef LOCAL
#define debug(...) cerr << "(" << #__VA_ARGS__ << "):", debug_out(__VA_ARGS__)
#else
#define debug(...) 47
#endif
const int MAX_N = 1e3 + 5;
vector<double> a, b;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
a.resize(n); b.resize(n);
for (int i = 0; i < n; i++) cin >> a[i] >> b[i];
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
double mx = 0;
double res_a = 0;
for (int i = 0; i <= n; i++) {
if (i) res_a += a[i - 1];
double res_b = 0;
for (int j = 0; j <= n; j++) {
if(j) res_b += b[j - 1];
mx = max(mx, min(res_a, res_b) - i - j);
}
}
cout << fixed << setprecision(4) << mx << '\n';
return 0;
}
