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#include <iostream>

using namespace std;

int n, k, res, a[1003];
bool changed = true;

bool check_good_and_fix(int* tab, int i) {
    bool changed = false;
    if(i > 0 && tab[i - 1] > tab[i] + k) {
        res += (tab[i - 1] - k) - tab[i];
        tab[i] = tab[i - 1] - k;
        changed = true;
    }
    if(i < n - 1 && tab[i + 1] > tab[i] + k) {
        res += (tab[i + 1] - k) - tab[i];
        tab[i] = tab[i + 1] - k;
        changed = true;
    }
    return changed;
}

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

    cin >> n >> k;
    for(int i = 0; i < n; i++) {
        cin >> a[i];
    }
    while(changed) {
        changed = false;
        for(int i = 0; i < n; i++) {
            changed = check_good_and_fix(a, i) || changed;
        }
    }
    cout << res << "\n";
}