#include <iostream>
#include <vector>
#include <algorithm>
#define int long long
#define abs(a) (a < 0 ? -a: a )
using namespace std;

vector<int> vals = vector<int>(0);
vector<int> comp = vector<int>(0);



signed main()
{
    ios_base::sync_with_stdio(0);
    int count, k;

    cin >> count >> k;

    for(int i =0; i < count; ++i)
    {
        int sth;
        cin >> sth;
        vals.push_back(sth);
    }

    sort(vals.begin(), vals.end());

    for(int i = 0; i < count; ++i)
    {
        comp.push_back(vals[i] - k * i);
    }

    sort(comp.begin(), comp.end());
    int a = comp[count/2];
    int sum = 0;

    for(int i = 0; i < count; ++i)
    {
        sum += abs((vals[i] - (i * k + a)));
    }

    cout << sum;

    return 0;
}