#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
int main()
{
	long long num,dist,pom;
	std::vector<long long> s;

	cin >> num >> dist;

	for(long long i = 0 ; i < num ; ++i)
	{
		cin >> pom;

		s.push_back(pom);
	}

	if(num == 1)
	{
		cout << 0 << endl;
		return 0;
	}

	sort(s.begin(),s.end());

	bool suda = (num %2 == 0)?true:false;
	long long pivot_add =num/2 -((suda) ? 1 : 0) ;
	long long pivot = s[pivot_add];

	long long exp,res = 0;
	exp = pivot;


	//za pivotem vcetne
	for(auto it = pivot_add ; it < s.size() ; it++)
	{
		res += abs(s[it] - exp); // potrebuje kladna cisla	
		exp += dist;
	}	
	exp = pivot-dist;
	//pred
	for(auto it = pivot_add-1 ; it >=0  ; it--)
	{
		res += abs(s[it] - exp); // potrebuje kladna cisla	
		exp -= dist;
	}	

	cout << res << endl;
	return 0;
}