#include <stdio.h>
#include <stdlib.h>
#include <math.h>

float gipotenuza(long long  a, long long  b,int k)
{
    return sqrt(k * k + (a - b)*(a - b));
}

void sort(long long * a,int size)
{
    for (int i = 0; i < size-1; ++i)
    {
        for (int j = i +1; j < size; ++j)
        {
            if (a[j] < a[j-1])
            {
                long long  tmp = a[j];
                a[j] = a[j-1];
                a[j-1] = tmp;
            }
        }
    }
}

int main()
{
    int n,k;
    scanf("%d %d", &n, &k);

    long long * a = (long long *)calloc(n,sizeof(long long));
    for (int i = 0; i < n; ++i)
    {
        scanf("%lld", &a[i]);
    }

    sort(a,n);

    double res = 0;
    for (int i = 1; i < n; ++i)
    {
        res += gipotenuza(a[i],a[i-1],k);
    }
    printf("%.4lf", res);
    return 0;
}