#include <bits/stdc++.h>

using namespace std;
int a = 1000000;
int N, K;
vector<int> v;
int Funkce(int m){
    int s = 0;
    for(int i=0;i<v.size();++i){
        s+=abs(v[i]-(i*K + m));
    }
    return s;
}

int BinarySearch(int l,int r){
    int m = (l+r)/2;
    while(l<r){
        if(Funkce(m-1) < Funkce(m+1)){
            r = m-1;
        }
        else{
            l = m+1;
        }
    }
    return Funkce(m);
}

int main() {

    cin >> N >> K;

    while (N--) {
        int i;
        cin >> i;
        i+=a;
        v.push_back(i);
    }
    sort(v.begin(), v.end());
    cout << BinarySearch(0,a*2) << endl;
    return 0;
}