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/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
Write your code in this editor and press "Run" button to compile and execute it.

*******************************************************************************/

#include <iostream>
#include <vector>
int main()
{
    int n, k;
    std::cin >> n >> k;
    long long cost = 0;
    std::vector <int> V(n);
    for (int i = 0; i < n; i++) {
        std::cin >> V[i];
    }
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n - 1; j++) {
            if(V[j] + k < V[j+1]){
                cost += V[j+1] - k - V[j];
                V[j] = V[j+1] - k;
            }
        }
        for (int j = 1; j < n; j++) {
            if(V[j] + k < V[j-1]){
                cost += V[j-1] - k - V[j];
                V[j] = V[j-1] - k;
            }
        }
    }
    std::cout << cost << '\n';
}