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#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define all(x) begin(x), end(x)
#define sz(x) int((x).size())
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

#ifdef LOCAL
auto operator<<(auto& o, auto x) -> decltype(x.first, o);
auto operator<<(auto& o, auto x) -> decltype(x.end(), o) {
  o << "{";
  for (int i = 0; auto y : x) o << ", " + !i++ * 2 << y;
  return o << "}"; }
auto operator<<(auto& o, auto x) -> decltype(x.first, o) {
  return o << "(" << x.first << ", " << x.second << ")"; }
void __print(auto... x) { ((cerr << x << " "), ...) << endl; }
#define debug(x...) __print("[" #x "]:", x)
#else
#define debug(...) 2137
#endif

int main() {
  cin.tie(0)->sync_with_stdio(0);

  int n, k;
  cin >> n >> k;
  vector<int> v(n);
  int ans = 0;
  for(int i = 0; i < n; i++) {
    cin >> v[i];
    if(v[i] < v[i - 1] - k) {
      ans += v[i - 1] - k - v[i];
      v[i] = v[i - 1] - k;
    } else {
      for(int j = i - 1; j >= 0; j--) {
        if(v[j] < v[j + 1] - k) {
          ans += v[j + 1] - k - v[j];
          v[j] = v[j + 1] - k;
        }
      }
    }
  }
  cout << ans << endl;
}