import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum NUM_ITERS = 300;

void main() {
  try {
    for (; ; ) {
      const N = readInt();
      auto A = new int[N];
      foreach (i; 0 .. N) {
        A[i] = readInt();
      }
      
      auto sums = new int[1 << N];
      foreach (i; 0 .. N) {
        foreach (p; 0 .. 1 << i) {
          sums[p | 1 << i] = sums[p] + A[i];
        }
      }
      const ASum = sums[(1 << N) - 1];
      
      auto dp1 = new real[][](1 << N, ASum + 1);
      auto dp0 = new real[][](1 << N, ASum + 1);
      foreach (x; 0 .. ASum + 1) {
        dp1[0][x] = dp0[0][x] = (x > ASum - x) ? 1.0L : 0.0L;
      }
      foreach (p; 1 .. 1 << N) {
        auto app = new bool[ASum + 1];
        const sup = ((1 << N) - 1) ^ p;
        for (int q = sup; ; --q &= sup) {
          app[sums[q]] = true;
          if (q == 0) {
            break;
          }
        }
        foreach (x; 0 .. ASum + 1) {
          if (app[x]) {
            real f1 = 1.0L, f0 = 0.0L;
            foreach (iter; 0 .. NUM_ITERS) {
              f1 = 0.0L;
              foreach (i; 0 .. N) {
                if (p & 1 << i) {
                  chmax(f1, (1.0L / A[i]) * dp0[p ^ 1 << i][x + A[i]] + (1.0L - 1.0L / A[i]) * f0);
                }
              }
              f0 = 1.0L;
              foreach (i; 0 .. N) {
                if (p & 1 << i) {
                  chmin(f0, (1.0L / A[i]) * dp1[p ^ 1 << i][x] + (1.0L - 1.0L / A[i]) * f1);
                }
              }
            }
            dp1[p][x] = f1;
            dp0[p][x] = f0;
          }
        }
      }
      writefln("%.12f", dp1[(1 << N) - 1][0]);
    }
  } catch (EOFException e) {
  }
}