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#include <algorithm>
#include <bitset>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>

using namespace std;

#define PB push_back
#define MP make_pair
#define F first
#define S second
#define ALL(x) (x).begin(),(x).end()
#define SIZE(x) (int)(x).size()
#define CLEAR(tab) memset(tab, 0, sizeof(tab))
#define REP(x, n) for(int x = 0; x < (n); x++)
#define FOR(x, b, e) for(int x = (b); x <= (e); x++)
#define FORD(x, b, e) for(int x = (b); x >= (e); x--)
#define VAR(v, n) __typeof(n) v = (n)
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define DEBUG(fmt, ...) fprintf(stderr, fmt, ##__VA_ARGS__)

typedef long long int LL;
typedef pair<int,int> PII;
typedef vector<int> VI;

const int MXN = 1010;
const int C = 262144;
const int INF = 1000000001;
const int MOD = 1000000007;

int n, k;
int a[MXN];

int main() {
	scanf("%d %d", &n, &k);

	FOR(i, 1, n)
		scanf("%d", &a[i]);
	LL res = 0;
	FOR(_, 1, n) {
		FOR(i, 1, n - 1)
			if(a[i + 1] - a[i] > k) {
				res += a[i + 1] - k - a[i];
				a[i] = a[i + 1] - k;
			}
		FORD(i, n, 2)
			if(a[i - 1] - a[i] > k) {
				res += a[i - 1] - k - a[i];
				a[i] = a[i - 1] - k;
			}
	}
	printf("%lld\n", res);
	return 0;
}