#include <bits/stdc++.h>

using namespace std;

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);

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

    vector<int> a(n);

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

    long long answer = 0;

    vector<int> visited(n);
    priority_queue<pair<int, int>> current;

    for (int i = 0; i < n; ++i) current.emplace(a[i], i);

    while (!current.empty())
    {
        auto [_, i] = current.top();
        current.pop();

        if (visited[i]) continue;

        if (i > 0 && a[i - 1] + k < a[i])
        {
            answer += a[i] - a[i - 1] - k;
            a[i - 1] = a[i] - k;
            current.emplace(a[i - 1], i - 1);
        }
        if (i < n - 1 && a[i + 1] + k < a[i])
        {
            answer += a[i] - a[i + 1] - k;
            a[i + 1] = a[i] - k;
            current.emplace(a[i + 1], i + 1);
        }
    }

    cout << answer << '\n';
}