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

#define ll long long

using namespace std;

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

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

int main(){
    cin >> n >> d;
    
    for(ll i=0;i<n;i++){
        cin >> arr[i];
        arr[i] += 1000004;
    }

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

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