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

#define _TST 0
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+_TST];

	long long exp,res = 0;
	// exp = pivot;
	exp = pivot - dist * pivot_add;
	for (auto& n : s) {
		res += abs(n - exp);
		exp += dist;
	}


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

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