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#include <bits/stdc++.h>

using namespace std;

int main() {
    int n, k;
    cin >> n >> k;

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

    int res = 0;
    for (size_t i = 1; i < n; ++i) {
        const int diff = v[i] - v[i - 1];
        const int to_add = abs(min(0, diff + k));
        /*
        if (diff < -k) {
            res += abs(diff + k);
        }
        */
        v[i] += to_add;
        res += to_add;
    }
    for (int i = n - 2; i >= 0; --i) {
        const int diff = v[i] - v[i + 1];
        const int to_add = abs(min(0, diff + k));
        /*
        if (diff < -k) {
            res += abs(diff + k);
        }
        */
        v[i] += to_add;
        res += to_add;
    }

    cout << res << endl;
}