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//#pragma GCC optimize("O3")
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
using namespace std;
namespace debug {
template <class c> struct rge { c b, e; };
template <class c> rge<c> range(c i, c j) { return rge<c>{i, j}; }
template <class c> char spk(...);
template <class c> auto spk(c *a) -> decltype(cerr << *a, 0);
struct stream {
  ~stream() { cerr << endl; }
  template <class c>
  typename enable_if<sizeof spk<c>(0) != 1, stream &>::type operator<<(c i) {
    cerr << boolalpha << i;
    return *this;
  }
  template <class c>
  typename enable_if<sizeof spk<c>(0) == 1, stream &>::type operator<<(c i) {
    return *this << range(begin(i), end(i));
  }
  template <class a, class b> stream &operator<<(pair<a, b> p) {
    return *this << "(" << p.first << ", " << p.second << ")";
  }
  template <class c> stream &operator<<(rge<c> d) {
    *this << "[";
    for (auto it = d.b; it != d.e; it++)
      *this << ", " + 2 * (it == d.b) << *it;
    return *this << "]";
  }
  stream &_dbg(const string &s, int i, int b) { return *this; }
  template <class c, class... cs>
  stream &_dbg(const string &s, int i, int b, c arg, cs... args) {
    if (i == (int)(s.size()))
      return (*this << ": " << arg);
    b += (s[i] == '(') + (s[i] == '[') + (s[i] == '{') - (s[i] == ')') -
         (s[i] == ']') - (s[i] == '}');
    return (s[i] == ',' && b == 0)
               ? (*this << ": " << arg << "     ")._dbg(s, i + 1, b, args...)
               : (s[i] == ' ' ? *this : *this << s[i])
                     ._dbg(s, i + 1, b, arg, args...);
  }
};
} // namespace debug
#ifdef DEBUG
#define dout debug::stream()
#define dbg(...) ((dout << "line:" << __LINE__ << " >> ")._dbg(#__VA_ARGS__, 0, 0, __VA_ARGS__))
#else
#define dout
#define dbg(...)
#endif
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (b); i >= (a); i--)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define all(a) (a).begin(), (a).end()
#define SZ(x) (int)(x).size()
#define mp make_pair
#define st first
#define nd second
using ll = long long;
using pii = pair<int,int>;
using vi = vector<int>;



int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    int n, k;
    cin >> n >> k;
    vector<int> A(n);
    vector<bool> vis(n);
    rep(i, 0, n-1) cin >> A[i];
    vi B = A;
    priority_queue<pair<int, int>> Q;
    rep(i, 0, n-1) Q.emplace(B[i], i);
    while (!Q.empty()) {
        int i = Q.top().nd;
        Q.pop();
        if (vis[i]) continue;
        vis[i] = true;
        dbg(i, B[i]);
        for (int d: {-1, 1}) {
            int j = i + d;
            if (j >= 0 && j < n && B[j] < B[i] - k) {
                B[j] = B[i] - k;
                Q.emplace(B[j], j);
            }
        }
    }
    int ans = 0;
    rep(i, 0, n-1) ans += B[i] - A[i];
    cout << ans << '\n';
    return 0;
}