#include <iostream>
#include <algorithm>
#define MOD 1000000007

#define ll long long

using namespace std;

ll arr[1000000];
// ll sorter[2000000]
ll begs[1000000];
int n;
int d;

// void linsort(ll* a, ll* b){
//     ll* start = a;
//     for (int i=0; i<2000000; i++){
//         begs[i] = 0;
//     }
//     while(a!=b){
//         begs[*a] = 1;
//     }
//     for(int i=0;i)
// }

ll labs(ll a){
    return a<0?-a:a;
}

ll lmin(ll a, ll b){
    return a<b?a:b;
}

ll shift(int beg){
    ll sum = 0;
    ll pos = beg;
    for (int i=0;i<n;i++){
        sum += labs(arr[i]-pos);
        pos += d;
    }
    return sum;
}

int main(){
    cin >> n >> d;
    
    for(int i=0;i<n;i++){
        cin >> arr[i];
    }

    sort(arr, arr+n);
    for(int i=0;i<n;++i){
        begs[i] = arr[i]-i*d;
    }
    sort(begs, begs+n);

    cout << shift(begs[n/2]) << endl;
}