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#include<iostream>
#include<vector>

using namespace std;

int main() {
  ios_base::sync_with_stdio(false);

  int n, k;
  cin >> n >> k;

  int result = 0;
  vector<int> road(n);
  for(int i = 0; i < n; i++) {
    cin >> road[i];
  }

  for(int i = 1; i < n; i++) {
    int dif = road[i-1] - road[i];
    if(dif > k) {
      road[i] += dif-k;
      result += dif-k;
    } else if (-dif > k) {
      road[i-1] += -dif-k;
      result += -dif-k;
    }
  }

  for(int i = n-1; i > 0; i--) {
    int dif = road[i-1] - road[i];
    if(dif > k) {
      road[i] += dif-k;
      result += dif-k;
    } else if (-dif > k) {
      road[i-1] += -dif-k;
      result += -dif-k;
    }
  }

  cout << result << endl;
}