#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> p_ll;

template<class T>
void debug(T itr1, T itr2) { auto now = itr1; while(now<itr2) { cout << *now << " "; now++; } cout << endl; }
#define repr(i,from,to) for (ll i=(ll)from; i<(ll)to; i++)
#define all(vec) vec.begin(), vec.end()
#define rep(i,N) repr(i,0,N)
#define per(i,N) for (int i=(int)N-1; i>=0; i--)

const ll MOD = pow(10,9)+7;
const ll LLINF = pow(2,61)-1;
const int INF = pow(2,30)-1;

vector<ll> fac;
void c_fac(int x=pow(10,6)+10) { fac.resize(x,true); rep(i,x) fac[i] = i ? (fac[i-1]*i)%MOD : 1; }
ll modpow(ll x, ll p) { ll result = 1, now = 1, pm = x; while (now<=p) { if (p&now) { result = result * pm % MOD; } now*=2; pm = pm*pm % MOD; } return result; }
ll inv(ll a, ll m=MOD) { ll b = m, x = 1, y = 0; while (b!=0) { int d = a/b; a -= b*d; swap(a,b); x -= y*d; swap(x,y); } return (x+m)%m; }
ll nck(ll n, ll k) { return fac[n]*inv(fac[k]*fac[n-k]%MOD)%MOD; }
ll gcd(ll a, ll b) { if (a<b) swap(a,b); return b==0 ? a : gcd(b, a%b); }
ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }


int main() {
  ll N; cin >> N;
  double A[N]; rep(i,N) cin >> A[i];

  ll p3[N+1] = {}; rep(i,N+1) p3[i] = i==0 ? 1 : p3[i-1]*3;
  ll ma = p3[N];
  double dp[ma][2] = {};
  per(i,ma) {
    ll ti = i, c0 = 0, xsum = 0, ysum = 0, now[N];
    rep(j,N) { 
      now[j] = ti%3; ti/=3; 
      if (now[j]==0) c0++;
      else if (now[j]==1) xsum += A[j];
      else if (now[j]==2) ysum += A[j];
    }

    // cout << i << " " << c0 << " " << xsum << " " << ysum << endl;
    if (c0==0) {
      if (xsum>ysum) { dp[i][0] = 1; dp[i][1] = 1; }
      else { dp[i][0] = 0; dp[i][1] = 0; }
    }
    else {
      double rxy0 = 0, rxy1 = 0;
      rep(x,N) {
        if (now[x]) continue;
        double rx0 = 1, rx1 = 1;
        rep(y,N) {
          if (now[y]) continue;
          double r0 = (A[y]*dp[i+p3[x]][1]+(A[x]-1)*dp[i+p3[y]*2][0]) / (A[x]+A[y]-1);
          double r1 = ((A[y]-1)*dp[i+p3[x]][1]+A[x]*dp[i+p3[y]*2][0]) / (A[x]+A[y]-1);
          // cout << i << "->" << x << " " << y << " " << result << endl;
          rx0 = min(rx0,r0); rx1 = min(rx1,r1);
        }
        rxy0 = max(rxy0, rx0); rxy1 = max(rxy1, rx1);
      }
      dp[i][0] = rxy0; dp[i][1] = rxy1;
    }
  }

  // rep(i,ma) cout << dp[i][0] << " "; cout << endl;
  // rep(i,ma) cout << dp[i][1] << " "; cout << endl;
  double result = dp[0][0];
  cout << setprecision(10) << result << endl;
  return 0;
}