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#include <bits/stdc++.h>

using namespace std;

#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(...) {}
#endif

#define x first
#define y second
#define ir(x, a, b) ((a) <= (x) && (x) <= (b))
#define vec vector
#define rep(i, a, b) for (ll i = a; i < (b); ++i)
#define all(x) (x).begin(), (x).end()

using ll = long long;

int main() {
  cin.tie(0)->sync_with_stdio(0);
  ll N, K; cin >> N >> K;
  vec<ll> a(N);
  rep (n, 0, N) cin >> a[n];
  ll s = 0;
  rep (n, 0, 2*N) {
    rep (n, 0, N) {
      if (n > 0 && a[n] + K < a[n-1]) {
        s -= a[n];
        a[n] = a[n-1] - K;
        s += a[n];
      }
      if (n < N-1 && a[n] + K < a[n+1]) {
        s -= a[n];
        a[n] = a[n+1] - K;
        s += a[n];
      }
    }
  }
  cout << s << "\n";
  return 0;
}