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#include <stdio.h>
#include <time.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include <map> 
#include <string>
#include <vector>  
#include <iostream> 
#include <sstream> 
#include <queue>
#include <algorithm>
#include <assert.h>
#include <set>


using namespace std;

#define ll long long
#define PB 		push_back
#define FOR(a,start,end) 	for(int a=int(start); a<int(end); a++)
#define INF 		INT_MAX
#define SORT(a) 	sort(a.begin(),a.end()) 
#define CL(a,x) 		memset(a,x,sizeof(a))
#define REP(a,x)	for(int a=0;a<x;a++)
#define REP1(a,x)	for(int a=1;a<=x;a++)
#define MP 		make_pair



typedef vector<ll>     vi;
typedef pair<ll, ll>     pii;
typedef vector<string> vs;
typedef vector<pii> vii;
typedef vector<vector<ll> > vvi;
typedef vector<vector<string> > vvs;
typedef vector<pair<string, string> > vss;
typedef pair<string, string> pss;
typedef pair<ll, pii> ppii;
typedef vector<ppii> vppii;
typedef vector<vector<pii> > vvii;
typedef vector<vvi> vvvi;


ll  n, k, q, d, r, g, b, z, p, a, c;

vi vk, va, vd, vb;
vvi vva, vvk, vvd;
vii vax, vcx;
vvii vvax, vvbx;
pii p1, p2;
string w;
int ik;
priority_queue<pii> pq;

int main() {
	//freopen("c:\\wojtek\\uva\\pa\\debug\\t1.in", "rt", stdin);
	//freopen("c:\\cygwin64\\home\\plwokow\\.check_sol\\zb1\\in\\320.in", "rt", stdin);
	//d = 1000000007;
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(NULL);

	cin >> n >> k;
	va.assign(n, 0);
	//vax.assign(n,MP(0, 0));
	while (!pq.empty())
		pq.pop();
	for (int i = 0; i < n; i++) {
		cin >> va[i];
		pq.push(MP(va[i], i));
		//vax[i] = MP(va[i], i);
	}
	//SORT(vax);
	a = 0;
	while(!pq.empty()){
		pii p1 = pq.top();
		pq.pop();
		if (p1.first != va[p1.second])
			continue;
		int j = p1.second;
		if ((j > 0) && ((va[j] - va[j - 1]) > k)) {
			a += (va[j] - k - va[j - 1]);
			va[j - 1] = va[j] - k;
			pq.push(MP(va[j - 1], j - 1));
		}
		if((j<(n-1))&& ((va[j] - va[j + 1]) > k)) {
			a += (va[j] - k - va[j + 1]);
			va[j + 1] = va[j] - k;
			pq.push(MP(va[j + 1], j + 1));
		}
	}
	cout << a << '\n';

	return 0;

}