#include <iostream>
#include <set>
#include <vector>

using namespace std;

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

    int n;
    cin >> n;
    int k;
    cin >> k;

    vector<int> a(n);
    set<pair<int, int>> pq;

    for (int i = 0; i < n; i++) {
        cin >> a[i];
        pq.insert({a[i], i});
    }

    long long result = 0;

    while (!pq.empty()) {
        // cout << "pq: " << endl;
        // for (const auto& p : pq) {
        //     cout << "  " << p.first << ", " << p.second << endl;
        // }

        auto max = prev(pq.end());
        auto [maxValue, maxIndex] = *max;
        pq.erase(max);
        // cout << "max: " << maxValue << ", " << maxIndex << endl;

        if (maxIndex > 0) {
            int prev = a[maxIndex - 1];
            // cout << "prev: " << prev << endl;
            if (maxValue - prev > k) {
                int newPrev = maxValue - k;
                // cout << "newPrev: " << newPrev << endl;
                result += newPrev - prev;
                pq.erase({prev, maxIndex - 1});
                pq.insert({newPrev, maxIndex - 1});
                a[maxIndex - 1] = newPrev;
            }
        }

        if (maxIndex < n - 1) {
            int next = a[maxIndex + 1];
            // cout << "next: " << next << endl;
            if (maxValue - next > k) {
                int newNext = maxValue - k;
                // cout << "newNext: " << newNext << endl;
                result += newNext - next;
                pq.erase({next, maxIndex + 1});
                pq.insert({newNext, maxIndex + 1});
                a[maxIndex + 1] = newNext;
            }
        }
    }

    cout << result << endl;
}