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


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

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

    vector<int> a(n);
    long long initial = 0;
    for (int i=0; i<n; i++) {
        cin >> a[i];
        initial += a[i];
    }

    for (int i=1; i<n; i++) {
        if (abs(a[i] - a[i-1]) <= k) continue;
        else if (a[i] < a[i-1]) {
            a[i] += a[i-1] - a[i] - k;
        }
        else {
            int j = i-1;
            while (j >= 0 && a[j+1] - a[j] > k) {
                a[j] += a[j+1] - a[j] - k;
                j--;
            }
        }
    }

    long long result = 0;
    for (auto x: a) {
        result += x;
    }

    cout << result - initial << "\n";

    return 0;
}