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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()
#define YES cout << "YES\n"
#define NO cout << "NO\n"
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef long double ld;

#ifdef LOCAL
#define DTP(x, y)                                    \
    auto operator<<(auto &o, auto a)->decltype(y, o) \
    {                                                \
        o << "(";                                    \
        x;                                           \
        return o << ")";                             \
    }
DTP(o << a.first << ", " << a.second, a.second);
DTP(for (auto i : a) o << i << ", ", all(a));
void dump(auto... x) { ((cerr << x << ", "), ...) << '\n'; }
#define debug(x...) cerr << setw(4) << __LINE__ << ":[" #x "]: ", dump(x)
#else
#define debug(...) 42
#endif

stringstream os;
void testing()
{
    /*
        Here create tests by pushing to os (<<).
    */
    os = stringstream();
    os.seekg(0, ios::beg);
    cin.rdbuf(os.rdbuf());
}

void solve()
{
    ll n, k;
    cin >> n >> k;
    vl V(n), C(n, 0);
    for (auto &a : V)
        cin >> a;
    ll sum = 0;
    for (int i = 0; i < n; i++)
    {
        int it = 0;
        while (C[it])
            it++;
        for (int j = it + 1; j < n; j++)
            if (!C[j] && V[j] > V[it])
                it = j;
        if (it < n - 1 && V[it] - V[it + 1] > k)
        {
            sum += (V[it] - k - V[it + 1]);
            V[it + 1] = V[it] - k;
        }
        if (it && V[it] - V[it - 1] > k)
        {
            sum += (V[it] - k - V[it - 1]);
            V[it - 1] = V[it] - k;
        }
        C[it] = 1;
        // debug(V);
        // debug(it, sum);
    }
    cout << sum << endl;
}

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

    int Z = 1;
    // cin >> Z;
    while (Z--)
        solve();
}