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#include <bits/stdc++.h>
using namespace std;

const int MAX_N = 1005;
int a[MAX_N];

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

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

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

    int res = 0;

    for (int i = 1; i < n; i++) {
        int target = max(a[i], a[i - 1] - k);
        res += target - a[i];
        a[i] = target;
    }

    for (int i = n - 2; i >= 0; i--) {
        int target = max(a[i], a[i + 1] - k);
        res += target - a[i];
        a[i] = target;
    }

    cout << res << endl;

    return 0;
}