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#include <bits/stdc++.h>
#define F first
#define S second
#define pii pair<int, int>
using namespace std;
using ll = long long;
using ld = long double;

constexpr int SIZE = 1e3+3;

int tab[SIZE];
int k;
ll res;

void CHECK(int v){
	if (!v) return;
	if (tab[v]+k >= tab[v+1]) return;

	res += tab[v+1]-tab[v]-k;
	tab[v] = tab[v+1]-k;

	CHECK(v-1);
	return;
}

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

    int n;
    cin >> n >> k;

	for (int i=1; i<=n; i++) cin >> tab[i];

	res = 0;

	for (int i=1; i<n; i++){
		if (tab[i]+k >= tab[i+1] && tab[i]-k <= tab[i+1]) continue;
		if (tab[i]+k < tab[i+1]) CHECK(i);
		else {
			res += tab[i]-tab[i+1]-k;
			tab[i+1] = tab[i]-k;
		}
	}

	cout << res;

return 0;}