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#include <bits/stdc++.h>
using namespace std;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n, k; cin >> n >> k;
    vector<int> a(n);
    int s = 0;
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        s += a[i];
        for (int j = i - 1; j >= 0; j--) {
            a[j] = max(a[j], a[j + 1] - k);
        }
        if (i) {
            a[i] = max(a[i], a[i - 1] - k);
        }
    }
    cout << accumulate(a.begin(), a.end(), 0) - s;
}