#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cmath>
#include <map>
#include <queue>
#include <iomanip>
#include <set>
#include <tuple>
#define mkp make_pair
#define mkt make_tuple
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define all(v) v.begin(),v.end()
using namespace std;
typedef long long ll;
const ll MOD=1e9+7;
template<class T> void chmin(T &a,const T &b){if(a>b) a=b;}
template<class T> void chmax(T &a,const T &b){if(a<b) a=b;}

int N;
vector<int> A;

typedef tuple<int,int,int> TP;
map<TP,double> mp;

double solve(int c,int state,int win){
  TP tmp=mkt(c,state,win);
  if(mp.count(tmp)) return mp[tmp];
  if(state==0){
    int s=0,t=0;
    rep(i,N){
      if(win&(1<<i)) s+=A[i];
      else t+=A[i];
    }
    if((c==0&&s>t)||(c==1&&s<=t)) return mp[tmp]=1;
    else return mp[tmp]=0;
  }

  double res=0;
  for(int a=0;a<N;a++){
    if((state&(1<<a))==0) continue;

    if(A[a]==1){
      int nw=win;
      if(c==0) nw^=(1<<a);
      chmax(res,(1-solve(1-c,state^(1<<a),nw)));
      continue;
    }
    double score=1;
    for(int b=0;b<N;b++){
      if((state&(1<<b))==0) continue;

      double coef=(A[a]*A[b])/(double)(A[a]+A[b]-1);
      double val=0;
      if(c==0){
        val+=coef*(1-solve(1-c,state^(1<<a),win^(1<<a)))/A[a];
        val+=coef*(solve(c,state^(1<<b),win))*((A[a]-1)/(double)A[a])/A[b];
      }else{
        val+=coef*(1-solve(1-c,state^(1<<a),win))/A[a];
        val+=coef*(solve(c,state^(1<<b),win^(1<<b)))*((A[a]-1)/(double)A[a])/A[b];
      }
      chmin(score,val);
    }
    chmax(res,score);
  }
  return mp[tmp]=res;
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin>>N;
  A.resize(N);
  rep(i,N) cin>>A[i];

  double ans=solve(0,(1<<N)-1,0);
  cout<<fixed<<setprecision(10)<<ans<<endl;

  return 0;
}