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#include <bits/stdc++.h>

using namespace std;

#define vec vector


int main() {
  int n, k; cin >> n >> k;


  vec<int> a(n);
  for (int i = 0; i < n; i++) cin >> a[i];


  int res = 0;
  for (int j = 0; j < n; j++) {
    if (a[1] - k > a[0]) {
      res += a[1] - k - a[0];
      a[0] = a[1] - k;
    }
    if (a[n - 2] - k > a[n - 1]) {
      res += a[n - 2] - k - a[n - 1];
      a[n - 1] = a[n - 2] - k;
    }
    for (int i = 1; i < n - 1; i++) {
      int new_ = max(a[i - 1] - k, a[i + 1] - k);
      if (new_ > a[i]) {
        res += new_ - a[i];
        a[i] = new_;
      }
    }
  }
  cout << res << "\n";
}