#pragma GCC optimize "O3"
#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;

#define FOR(i,b,e) for(int i=b; i<=e; i++)
#define FORD(i,b,e) for(int i=b; i>=e; i--)
#define SIZE(x) ((int)x.size())
#define pb push_back
#define st first
#define nd second
#define sp ' '
#define ent '\n'

int n, k;
vector<ll> ziom;

ll licz(ll val){
	ll ret=0;
	FOR(i, 0, n-1) ret+=abs(ziom[i]-val-(ll)i*k);
	return ret;
}


void solve(){
	int a;
	cin>>n>>k;
	if(n==1){
		cout<<0<<ent;
		return;
	}
	FOR(i, 1, n){
		cin>>a;
		ziom.pb(a);
	}
	sort(ziom.begin(), ziom.end());
	ll l, r, mid1, mid2, ans1, ans2;
	l=r=1e12+5*(1e11);
	l*=-1;
	while(l+2<r){
		mid1=(l*2+r)/3;
		mid2=(l+r*2)/3;
		ans1=licz(mid1);
		ans2=licz(mid2);
		if(ans1<ans2) r=mid2;
		else l=mid1;
	}
	cout<<min({licz(l), licz(l+1), licz(l+2)})<<ent;
}

int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	solve();
	return 0;
}

/*
10 4
140 26 69 55 39 64 2 89 78 421
*/