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#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

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

    int n;
    long long k;
    if (!(cin >> n >> k)) return 0;

    vector<long long> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }

    vector<long long> original = a;
    bool changed = true;
    while (changed) {
        changed = false;
        for (int i = 1; i < n; i++) {
            if (a[i] < a[i - 1] - k) {
                a[i] = a[i - 1] - k;
                changed = true;
            }
        }
        for (int i = n - 2; i >= 0; i--) {
            if (a[i] < a[i + 1] - k) {
                a[i] = a[i + 1] - k;
                changed = true;
            }
        }
    }

    long long total_gravel = 0;
    for (int i = 0; i < n; i++) {
        total_gravel += (a[i] - original[i]);
    }

    cout << total_gravel << endl;

    return 0;
}