#include <bits/stdc++.h>
using namespace std;
vector<long long> v;
vector<long long> v2;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int a;
    long long b,pocz=-2e12,c;
    cin>>a>>b;
    for(int x=0;x<a;x++)
    {
        cin>>c;
        v.push_back(c);
    }
    sort(v.begin(),v.end());
    for(auto x:v)
    {
        v2.push_back(pocz-x);
       // cout<<pocz<<'\n';
        pocz+=b;
    }
    sort(v2.begin(),v2.end());
    long long suma=0;
    long long pom=v2[a/2];
    for(auto x:v2)
    {
        suma+=abs(x-pom);
       // cout<<abs(x-pom)<<'\n';
    }
    cout<<suma;
    return 0;
}