#include <bits/stdc++.h>

using namespace std;

typedef long long int LL;

const int N = 1e6 + 7;

int n, k;
int in[N];
LL minim[N];

int main(){
	scanf("%d %d", &n, &k);
	for(int i = 1; i <= n; ++i)
		scanf("%d", &in[i]);
	sort(in + 1, in + n + 1);
	
	for(int i = 1; i <= n; ++i)
		minim[i] = in[i] - 1LL * i * k;
	sort(minim + 1, minim + n + 1);
	
	LL ans = 0;
	LL start = minim[(n + 1) / 2];
	for(int i = 1; i <= n; ++i)
		ans += abs(in[i] - (start + 1LL * i * k));
	printf("%lld\n", ans);
	return 0;
}