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

using namespace std;

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

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

    vector<int> a(n + 2);

    for (int i = 1; i <= n; ++i)
    {
        cin >> a[i];
    }

    int res = 0;

    while (true)
    {
        bool found = false;

        for (int i = 1; i <= n; ++i)
        {
            int h = max(a[i - 1], a[i + 1]);

            if (a[i] + k < h)
            {
                int c = h - (a[i] + k);

                a[i] += c;
                res += c;

                found = true;
            }
        }

        if (!found)
            break;
    }

    cout << res << "\n";

    return 0;
}