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

const int MAX_N = 1e3 + 3;
int h[MAX_N];
int vis[MAX_N];
int n, k;

int new_max() {
    int _max = 0;
    for (int i = 1; i <= n; i++) {
        if (!vis[i]) {
            if (h[i] > h[_max]) {
                _max = i;
            }
        }
    }
    return _max;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int act;
    int ans = 0;
    cin >> n >> k;
    for (int i = 1; i <= n; i++) {
        cin >> h[i];
    }
    for (int i = 1; i <= n; i++) {
        act = new_max();
        vis[act] = true;
        if (act - 1 > 0 && h[act] > h[act - 1]) {
            if (h[act] - h[act - 1] > k) {
                ans += h[act] - k - h[act - 1];
                h[act - 1] += h[act] - k - h[act - 1];
            }
        }
        if (act + 1 <= n && h[act] > h[act + 1]) {
            if (h[act] - h[act + 1] > k) {
                ans += h[act] - k - h[act + 1];
                h[act + 1] += h[act] - k - h[act + 1];
            }
        }
        // for (int i = 1; i <= n; i++) {
        //     cout << h[i] << " ";
        // }
        // cout << "\n";
    }
    cout << ans << "\n";
	return 0;
}