#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
using namespace std;
int n, k, X[1000], suma;
int main()
{
    cin>> n >> k;
    for (int i=0; i<n; i++)
        cin>> X[i];
    for (int j=0; j<n; j++)
        for (int i=0; i<n-1; i++)
        {
            if (X[i]-X[i+1]>k)
                {
                    suma=suma+X[i]-k-X[i+1];
                    X[i+1]=X[i]-k;
                }
            if (X[i]-X[i+1]<-k)
                {
                    suma=suma+X[i+1]-k-X[i];
                    X[i]=X[i+1]-k;
                }
        }
    cout<< suma;
    //for (int i=0; i<n; i++)
    //  cout<< X[i] << " ";
    return 0;
}