#include <string>
#include <vector>
#include <list>
#include <cmath>
#include <algorithm>
#include <map>
#include <set>
#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;

#define VIT(i, v) for (i = 0; i < v.size(); i++) 
#define IT(it, ds) for (it = ds.begin(); it != ds.end(); it++)
#define O1(v) cout << v << endl
#define O2(v1, v2) cout << v1 << " " << v2 << endl
#define O3(v1, v2, v3) cout << v1 << " " << v2 << " " << v3 << endl
#define OVEC(v) { int iii; VIT(iii, v) cout << v[iii] << " " ; cout << endl; }
typedef vector <int> IVec;

class CtuRobots {
  public:
    double maxDist(int B, vector <int> cost, vector <int> cap);
    vector <double> CP;
    vector <int> CO;
    double MF(int index, int budget);
    vector < vector < double > > cache;
};

double CtuRobots::MF(int index, int budget)
{
  double dnot, dinc;
  if (index == CO.size()) return 0;

  if (cache[index][budget] != -1) return cache[index][budget];
  dnot = MF(index+1, budget);
  if (budget < CO[index]) {
    cache[index][budget] = dnot;
    return cache[index][budget];
  }

  dinc = (MF(index+1, budget - CO[index]) + CP[index]) / 3;
  cache[index][budget] = (dinc > dnot) ? dinc : dnot;
  return cache[index][budget];
}

double CtuRobots::maxDist(int B, vector <int> cost, vector <int> cap)
{
  int i;
  multimap <int, int> M;
  multimap <int, int>::iterator mit;
  double dist, best;
  
  VIT(i, cost) M.insert(make_pair(-cap[i], cost[i]));

  IT(mit, M) {
    CO.push_back(mit->second);
    CP.push_back(-mit->first);
  }

  cache.resize(cost.size()+1);
  VIT(i, cache) cache[i].resize(B+1, -1);

  best = 0;
  VIT(i, CP) {
    if (CO[i] <= B) {
      dist = (CP[i] + MF(i+1, B-CO[i]) ) / 2.0;
      if (dist > best) best = dist;
    }
  }

  return best;
}