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#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using ll = long long;
using sz = size_t;
using namespace std;

// make the code less c++-readable:
template<class T> using v = vector<T>; 
template<class T> using vv = v<v<T>>; 
using vi = v<int>; using vll = v<ll>; using vvi = vv<int>; using vvll = vv<ll>;

// hai loading utilities
#define $T template<class T>
#define $Ts template<class... T>
$T T Load() { T v; cin >> v; return v; }
$T auto Loads(int n) { v<T> v; v.reserve(n); while(n--) v.emplace_back(Load<T>()); return v; }
$T auto Loads() { return Loads<T>(Load<int>()); }
template<class T, int N> auto Loada() { array<T, N> a; for (T& v: a) v = Load<T>(); return a; }
$Ts auto Cols(int rows) { tuple<v<T>...> t; while(rows--) [&]<sz... I>(index_sequence<I...>){(std::get<I>(t).push_back(Load<T>()), ...);}(index_sequence_for<T...>{}); return t; }
//$Ts auto Rows(int rows) { v<tuple<T...>> v; while(rows--) { v.emplace_back(Load<T>()...); } return v; } bugged :(
struct _aIV { $T operator vector<T>() { return Loads<T>(n); } sz n; };
struct _aI { $T operator T() { return Load<T>(); } _aIV operator()(sz n) { return {n}; } }; static inline _aI $;  /* int N = $;  vi Y = $(N); */
#define MAKE_LOADER(T, alias) \
  T alias() { return Load<T>(); }   /* int x = Int(); */\
  auto alias##s() { return Loads<T>(); }   /* vector<> xs = Ints(); */\
  auto alias##s(int n) { return Loads<T>(n); }   /* vector<> xs = Ints(7); */\
  template<int N> auto alias##a() { return Loada<T, N>(); }   /* array<> xs = Inta<7>();  */\
// line intentionally left blank
MAKE_LOADER(int, Int)
MAKE_LOADER(long long, LL)
MAKE_LOADER(char, Char)
MAKE_LOADER(string, String)
// kthxbye

constexpr int MAX_H=1'000'000+44;

void test() {
    int N = $;
    int K = $;

    v<unordered_set<int>> WYS_IDX(MAX_H); // WYS[h]=… pozycje wysokie na h
    vi WYS(N); // aktualna wys.
    ll ans = 0;

    for (int i = 0; i < N; ++i) {
        WYS[i] = $;
        WYS_IDX[WYS[i]].insert(i);
    }

    for (int h = MAX_H-1; h > 0; --h) {
        while (WYS_IDX[h].size()) {
            auto it = WYS_IDX[h].begin();
            int x = *it;
            WYS_IDX[h].erase(it);

            for (int x2 : {x-1, x+1}) {
                if (x2 < 0 || x2 >= N) continue;

                int rozn = WYS[x] - WYS[x2];
                if (rozn > K) {
                    int dh = rozn - K;
                    WYS_IDX[WYS[x2]].erase(x2);
                    WYS[x2] += dh;
                    WYS_IDX[WYS[x2]].insert(x2);
                    ans += dh;
                }
            }
        }
    }

    cout << ans << endl;
}


[[maybe_unused]] void jeden_test() { test(); }
[[maybe_unused]] void wiele_test() { int T = $; while (T--) test(); }

int main() {
    jeden_test();
    return 0;
}