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#include <bits/stdc++.h>
using namespace std;
#define fwd(i, a, n) for (int i = (a); i < (n); i++)
#define rep(i, n) fwd(i, 0, n)
#define all(X) X.begin(), X.end()
#define sz(X) int(size(X))
#define pb push_back
#define eb emplace_back
#define st first
#define nd second
using pii = pair<int, int>; using vi = vector<int>;
using ll = long long; using ld = long double;
#ifdef LOC
auto SS = signal(6, [](int) { *(int *)0 = 0; });
#define DTP(x, y) auto operator << (auto &o, auto a) -> decltype(y, o) { o << "("; x; return o << ")"; }
DTP(o << a.st << ", " << a.nd, a.nd);
DTP(for (auto i : a) o << i << ", ", all(a));
void dump(auto... x) { (( cerr << x << ", " ), ...) << '\n'; }
#define deb(x...) cerr << setw(4) << __LINE__ << ":[" #x "]: ", dump(x)
#else
#define deb(...) 0
#endif


void solve() {
    int n,k;
    cin >> n >> k;
    multiset<pii> H;
    vector<int> C(n+1);
    for(int i = 1; i <= n; i++) {
        int x;
        cin >> x;
        C[i] = x;
        H.insert({x,i});
    }
    int res = 0;

    auto increase = [&H, &C, &res](int id, int h) {
        if(C[id] >= h) return;
        res += h - C[id];
        H.erase({C[id], id});
        C[id] = h;
        H.insert({C[id], id});
    };

    while(!H.empty()) {
        auto [h, id] = *H.rbegin();
        H.erase({h, id});
        if(id > 1) increase(id-1, h-k);
        if(id < n) increase(id+1, h-k); 
    }

    cout << res << "\n";
}

int32_t main() {
	cin.tie(0)->sync_with_stdio(0);
	cout << fixed << setprecision(10);

    solve();

}