import java.io.*;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

public class InversionsShuffle implements Runnable {

    BufferedReader in;
    PrintWriter out;
    StringTokenizer tok = new StringTokenizer("");

    void init() throws FileNotFoundException {
        try {
            in = new BufferedReader(new FileReader("input.txt"));
            out = new PrintWriter("output.txt");
        } catch (Exception e) {
            in = new BufferedReader(new InputStreamReader(System.in));
            out = new PrintWriter(System.out);
        }
    }

    String readString() throws IOException {
        while (!tok.hasMoreTokens()) {
            try {
                tok = new StringTokenizer(in.readLine(), " :");
            } catch (Exception e) {
                return null;
            }
        }
        return tok.nextToken();
    }

    int readInt() throws IOException {
        return Integer.parseInt(readString());
    }

    int[] readIntArray(int size) throws IOException {
        int[] res = new int[size];
        for (int i = 0; i < size; i++) {
            res[i] = readInt();
        }
        return res;
    }

    long readLong() throws IOException {
        return Long.parseLong(readString());
    }

    double readDouble() throws IOException {
        return Double.parseDouble(readString());
    }

    <T> List<T>[] createGraphList(int size) {
        List<T>[] list = new List[size];
        for (int i = 0; i < size; i++) {
            list[i] = new ArrayList<>();
        }
        return list;
    }

    public static void main(String[] args) {
        new Thread(null, new InversionsShuffle(), "", 1l * 200 * 1024 * 1024).start();
    }

    long timeBegin, timeEnd;

    void time() {
        timeEnd = System.currentTimeMillis();
        System.err.println("Time = " + (timeEnd - timeBegin));
    }

    long memoryTotal, memoryFree;

    void memory() {
        memoryFree = Runtime.getRuntime().freeMemory();
        System.err.println("Memory = " + ((memoryTotal - memoryFree) >> 10)
                + " KB");
    }

    public void run() {
        try {
            timeBegin = System.currentTimeMillis();
            memoryTotal = Runtime.getRuntime().freeMemory();
            init();
            solve();
            out.close();
            if (System.getProperty("ONLINE_JUDGE") == null) {
                time();
                memory();
            }
        } catch (Exception e) {
            e.printStackTrace();
            System.exit(-1);
        }
    }

    class Fenwick {
        long[] data;
        int n;

        public Fenwick(int n) {
            this.n = n;
            data = new long[n];
        }

        void add(int at, long val) {
            while (at < data.length) {
                data[at] += val;
                at |= at + 1;
            }
        }

        long get(int at) {
            long res = 0;
            while (at >= 0) {
                res += data[at];
                at = (at & (at + 1)) - 1;
            }
            return res;
        }
    }

    long calculateBaseInversionCount(int[] a) {
        long res = 0;
        Fenwick fenwick = new Fenwick(a.length + 1);
        for (int i = a.length - 1; i >= 0; i--) {
            res += fenwick.get(a[i]);
            fenwick.add(a[i], 1);
        }
        return res;
    }

    double averageInversionsCount(int k) {
        return (double) k * (k - 1) / 4;
    }

    void solve() throws IOException {
        int n = readInt();
        int[] a = readIntArray(n);
        Fenwick fenwick = new Fenwick(n + 1);
        double countOfSegments = (long) n * (n + 1) / 2;
        double expectedValueOfDifference = 0;
        long countInversionsOnSuffix = 0;
        double sumOfExpectedValues = 0;
        for (int i = n - 1; i >= 0; i--) {
            long lowerRight = fenwick.get(a[i]);
            countInversionsOnSuffix += lowerRight;
            sumOfExpectedValues += averageInversionsCount(n - i);
            expectedValueOfDifference += (sumOfExpectedValues - countInversionsOnSuffix) / countOfSegments;
            fenwick.add(a[i], n - i);
        }
        out.println(calculateBaseInversionCount(a) + expectedValueOfDifference);
    }

}