#include <bits/stdc++.h>
using namespace std;
#define EPS (1e-10)
#define REP (i,n) for (int i = 0; i<(n);i++)

typedef long double ld;
typedef long long ll;
typedef pair<int,int> ii;
typedef pair<double, double> dd;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<double> vd;

int main() {
    ios::sync_with_stdio(false);
    ll N, a; cin >> N >> a;
    vll V(N);
    for(long long i = 0; i < N; ++i) cin >> V[i];
    sort(V.begin(), V.end());

    long long lb = V[0], ub = V[N-1];
    while (ub-lb >= 3) {
        long long aa = lb+(ub-lb)/3;
        long long ab = ub-(ub-lb)/3;
        long long s1=0, s2=0;
        for(long long i = 0; i < N; ++i) {
            s1 += abs(V[i] - aa-i*a);
        }
        for(long long i = 0; i < N; ++i) {
            s2 += abs(V[i] - ab-i*a);
        }
        if (s1 > s2) lb = aa;
        else ub = ab;
        
    }
    // cout << lb << " " << ub << endl;
    ll res = LLONG_MAX;
    for(long long r = lb-4; r <= ub+4; ++r) {
        ll s2 = 0;
        for(long long i = 0; i < N; ++i) {
                s2 += abs(V[i] - r-i*a);
            }
        res = min(s2, res);
    }
    cout << res << endl;

}