package no1xxx;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;

public class No1151 {
	InputStream is;
	PrintWriter out;
	String INPUT = "";
	
	void solve()
	{
		int n = ni();
		int[] a = na(n);
		
		int O = 110;
		double[][][] P = new double[2][1<<n][2*O+1];
		for(int j = O+1;j <= 2*O;j++){
			P[0][0][j] = 1;
			P[1][0][j] = 1;
		}
		for(int i = 1;i < 1<<n;i++){
			int[] b = new int[Integer.bitCount(i)];
			int p = 0;
			for(int j = 0;j < n;j++){
				if(i<<~j<0){
					b[p++] = j;
				}
			}
			
			for(int j = 0;j <= 2*O;j++){
				double pl = 0, mi = 1;
				double[] h1 = new double[n];
				double[] h2 = new double[n];
				for(int k : b){
					h1[k] = (j+a[k] <= 2*O ? P[1][i^1<<k][j+a[k]] : 1.);
					h2[k] = (j-a[k] >= 0 ? P[0][i^1<<k][j-a[k]] : 0.);
				}
				for(int rep = 0;;rep++){
					double npl = 0, nmi = 1;
					for(int k : b){
						npl = Math.max(npl, (h1[k] - mi) / a[k] + mi);
						nmi = Math.min(nmi, (h2[k] - pl) / a[k] + pl);
//							if(i + 1 == 1<<n && rep == 10)tr(j, k, (j+a[k] <= 2*O ? P[1][i^1<<k][j+a[k]] : 1.) / a[k] + mi * (1-1./a[k]));
//							if(i + 1 == 1<<n && rep < 2)tr(j, k, (j-a[k] >= 0 ? P[0][i^1<<k][j-a[k]] : 0.) / a[k] + pl * (1-1./a[k]));
					}
					boolean end = Math.abs(pl - npl) + Math.abs(mi - nmi) < 1e-7;
					pl = npl;
					mi = nmi;
					if(end){
//						tr(i, j, rep);
						break;
					}
				}
				P[0][i][j] = pl;
				P[1][i][j] = mi;
			}
		}
		out.printf("%.14f\n", P[0][(1<<n)-1][O]);
	}
	
	void run() throws Exception
	{
//		int n = 10, m = 99999;
//		Random gen = new Random();
//		StringBuilder sb = new StringBuilder();
//		sb.append(n + " ");
//		for (int i = 0; i < n; i++) {
//			sb.append(gen.nextInt(20)+1 + " ");
//		}
//		INPUT = sb.toString();

		
		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		out = new PrintWriter(System.out);
		
		long s = System.currentTimeMillis();
		solve();
		out.flush();
		if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
//		Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){
//			@Override
//			public void run() {
//				long s = System.currentTimeMillis();
//				solve();
//				out.flush();
//				if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
//			}
//		};
//		t.start();
//		t.join();
	}
	
	public static void main(String[] args) throws Exception { new No1151().run(); }
	
	private byte[] inbuf = new byte[1024];
	public int lenbuf = 0, ptrbuf = 0;
	
	private int readByte()
	{
		if(lenbuf == -1)throw new InputMismatchException();
		if(ptrbuf >= lenbuf){
			ptrbuf = 0;
			try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
			if(lenbuf <= 0)return -1;
		}
		return inbuf[ptrbuf++];
	}
	
	private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
	private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
	
	private double nd() { return Double.parseDouble(ns()); }
	private char nc() { return (char)skip(); }
	
	private String ns()
	{
		int b = skip();
		StringBuilder sb = new StringBuilder();
		while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ')
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	
	private char[] ns(int n)
	{
		char[] buf = new char[n];
		int b = skip(), p = 0;
		while(p < n && !(isSpaceChar(b))){
			buf[p++] = (char)b;
			b = readByte();
		}
		return n == p ? buf : Arrays.copyOf(buf, p);
	}
	
	private int[] na(int n)
	{
		int[] a = new int[n];
		for(int i = 0;i < n;i++)a[i] = ni();
		return a;
	}
	
	private long[] nal(int n)
	{
		long[] a = new long[n];
		for(int i = 0;i < n;i++)a[i] = nl();
		return a;
	}
	
	private char[][] nm(int n, int m) {
		char[][] map = new char[n][];
		for(int i = 0;i < n;i++)map[i] = ns(m);
		return map;
	}
	
	private int[][] nmi(int n, int m) {
		int[][] map = new int[n][];
		for(int i = 0;i < n;i++)map[i] = na(m);
		return map;
	}
	
	private int ni() { return (int)nl(); }
	
	private long nl()
	{
		long num = 0;
		int b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}
		
		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}
	
	private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); }
}