#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);
    int N, a; cin >> N >> a;
    vi V(N);
    for(int i = 0; i < N; ++i) cin >> V[i];
    sort(V.begin(), V.end());
    int lb = V[0], ub = V[N-1];
    int res;
    while(lb <= ub) {
        int mid = (lb+ub)/2;
        ll c1 = 0, c2 = 0;
        for(int i = 0; i < N; ++i) {
            if (V[i] > mid + i*a) c1++;
            else if (V[i] < mid + i*a) c2++;
        }
        if (c1 == c2) {
            res = mid;
            break;
        }  else if (c1 < c2) {
            ub = mid-1;
        } else {
            lb = mid+1;
        }
    }
    ll ss = 0;
    // cout << res << endl;
    for(int i = 0; i < N; ++i) {
        ss += abs(V[i] - res-i*a);
    }
    cout << ss << endl;

}