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#include <cstdio>
#include <iostream>
#include <algorithm>
#include <set>
#include <map>
#include <stack>
#include <list>
#include <queue>
#include <deque>
#include <cctype>
#include <string>
#include <vector>
#include <sstream>
#include <iterator>
#include <numeric>
#include <cmath>
using namespace std;

typedef vector <int > VI;
typedef vector < VI > VVI;
typedef long long LL;
typedef vector < LL > VLL;
typedef vector < double > VD;
typedef vector < string > VS;
typedef pair<int,int> PII;
typedef vector <PII> VPII;
typedef istringstream ISS;

#define ALL(x) x.begin(),x.end()
#define REP(i,n) for (int i=0; i<(n); ++i)
#define FOR(var,pocz,koniec) for (int var=(pocz); var<=(koniec); ++var)
#define FORD(var,pocz,koniec) for (int var=(pocz); var>=(koniec); --var)
#define FOREACH(it, X) for(__typeof((X).begin()) it = (X).begin(); it != (X).end(); ++it)
#define PB push_back
#define PF push_front
#define MP(a,b) make_pair(a,b)
#define ST first
#define ND second
#define SIZE(x) (int)x.size()

const int N = 1010;
int wys[N];
set<pair<int, int> > s;
long long res;

void upd(int i, int w) {
	s.erase(make_pair(-wys[i], i));
	wys[i] = w;
	s.insert(make_pair(-wys[i], i));
}


int main(){
	int n, k;
	scanf("%d%d", &n, &k);
	for (int i = 0; i < n; ++i) {
		int a; scanf("%d", &a);
		wys[i] = a;
		s.insert(make_pair(-a, i));
	}
	for (int i = 0; i < n; ++i) {
		auto it = s.begin();
		pair<int, int> p = *it;
		s.erase(it);
		int j = p.second;
		int w = -p.first - k;
		if (j > 0 && w > wys[j-1]) {
			res += (long long)(w - wys[j-1]);
			upd(j-1, w);
		}
		if (j < n-1 && w > wys[j+1]) {
			res += (long long)(w - wys[j+1]);
			upd(j+1, w);
		}
	}
	cout << res << endl;
	return 0;
}