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#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
#include <string>

using namespace std;
using ll = long long;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    ll n, k;
    cin >> n >> k;
    vector<ll> h(n), s(n);
    for(ll i = 0; i < n; ++i){
        cin >> h[i];
        s[i] = h[i];
    }
    ll wyn = 0;
    vector<bool> on(n, 1);
    for (ll i = 0; i < n; ++i){
        ll p = -1;
        for (int j = 0; j < n; ++j){
            if (on[j]){
                if (p == -1 or h[p] < h[j]) p = j;
            }
        }
        ll a = -1, b = h[p], c = -1;
        on[p] = 0;
        if (p > 0){
            a = h[p - 1];
        }
        if (p < n - 1){
            c = h[p + 1];
        }
        if (b + k < max(a, c)){
            wyn += max(a, c) - b - k;
            b += max(a, c) - b - k;
            h[p] = b;
        }
        if (a + k < b and a != -1){
            wyn += b - k - a;
            a += b - k - a;
            h[p - 1] = a;
        }
        if (c + k < b and c != -1){
            wyn += b - k - c;
            c += b - k - c;
            h[p + 1] = c;
        }
    }
    cout << wyn << endl;
}