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#include <bits/stdc++.h>

using namespace std;
using LL = long long;
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#define REP(i, n) FOR(i, 0, (n) - 1)
#define ssize(x) int(x.size())

template<class A, class B> auto &operator<<(ostream &o, pair<A, B> p) {
    return o << '(' << p.first << ", " << p.second << ')';
}

template<class T> auto operator<<(ostream &o, T x) -> decltype(x.end(), o) {
    o << '{'; int i = 0; for (auto e : x) o << (", ")+2*!i++ << e;
    return o << '}';
}

#ifdef DEBUG
#define debug(x...) cerr << "[" #x "]: ", [](auto... $) {((cerr << $ << "; "), ...); }(x), cerr << '\n';
#else
#define debug(...) {}
#endif


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, k;
    cin >> n >> k;
    vector<int> a(n);
    set<pair<int, int>, greater<>> best;
    REP(i, n) {
        cin >> a[i];
        best.insert({a[i], i});
    }

    LL ans = 0;
    auto adjust = [&](int i, int neigh) {
        if (i < 0 || i >= n)
            return;

        int lacks = a[neigh] - a[i] - k;
        if (lacks > 0) {
            best.erase({a[i], i});
            ans += lacks;
            a[i] += lacks;
            best.insert({a[i], i});
        }
    };

    REP(j, n) {
        auto [_, i] = *best.begin();
        best.erase(best.begin());
        adjust(i - 1, i);
        adjust(i + 1, i);
    }

    cout << ans << '\n';

    return 0;
}