Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
double avg = 0;
int[] arr = new int[n];

arr[0] = sc.nextInt();
for (int i = 1; i < n; i++)
{
    arr[i] = sc.nextInt();
    avg += Math.abs(arr[i] - arr[i - 1]);
}

System.out.printf("%.2f\n", avg / (n - 1));