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

#define int int64_t

const int64_t mod = 1e9+7;
const int maxn = 1e3+10;
int inf;


/*
*/

int a[maxn];
int n, k;

priority_queue<pair<int, int>> pq;
int solve_by_pq()
{
    a[0] = 0;
    a[n+1] = 0;
    for (int i = 1; i <= n; i++)
    {
        pq.push({a[i], i});
    }

    int ans = 0;

    while (!pq.empty())
    {
        int cn = pq.top().second;
        pq.pop();

        if (cn < 1 || cn > n)
        {
            continue;
        }
        int to_add = max((int)0, max(a[cn-1] - k - a[cn], a[cn+1] - k - a[cn]));
        if (to_add == 0)
        {
            continue;
        }
        a[cn] += to_add;
        ans += to_add;

        pq.push({a[cn-1], cn-1});
        pq.push({a[cn+1], cn+1});
    }

    return ans;
}

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


    int ans = solve_by_pq();
    cout << ans << endl;
}

int32_t main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
	inf = numeric_limits<int>::max()/2;

    int T = 1;
    //cin >> T;
    while (T--) tc();

    return 0;
}