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#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    ll gravel = 0;
    ll n, max_diff;
    cin >> n >> max_diff;
    vector<ll> heights(n);
    for (ll i = 0; i < n; i++)
    {
        cin >> heights[i];
    }

    bool flag_changes = true;
    while (flag_changes == true)
    {
        flag_changes = false;
        for (ll i = 0; i < n - 1; i++)
        {
            if (heights[i] < heights[i + 1])
            {
                ll add = heights[i + 1] - heights[i] - max_diff;
                if (add > 0)
                {
                    flag_changes = true;
                    heights[i] += add;
                    gravel += add;
                }
            }
            else
            {
                ll add = heights[i] - heights[i + 1] - max_diff;
                if (add > 0)
                {
                    flag_changes = true;
                    heights[i + 1] += add;
                    gravel += add;
                }
            }
        }
    }
    cout << gravel << endl;
}