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/* -----------------------
Autor: Tomasz Boguslawski
-------------------------- */
#include<cstdio>
#include<cstdlib>
#include<iostream>
#include<fstream>
#include<iomanip>
#include<string>
#include<sstream>
#include<cstring>
#include<map>
#include<vector>
#include<set>
#include<queue>
#include<algorithm>
#include <fstream>
#include<math.h>

#define LL long long
#define FOR(x, b, e) for(LL x = b; x <= (e); x++)
#define FORS(x, b, e, s) for(LL x = b; x <= (e); x+=s)
#define FORD(x, b, e) for(LL x = b; x >= (e); x--)
#define VAR(v, n) __typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define DEBUG if (debug)
#define MIN(a,b) ((a>b)?b:a)
#define MAX(a,b) ((a>b)?a:b)

using namespace std;

LL w[10000];
LL n, k;

/// MAIN
int main(int argc, char* argv[])
{
    // magic formula, which makes streams work faster:
	ios_base::sync_with_stdio(0);
	cin >> n; cin >> k;
	FOR(i,1,n) cin >> w[i];
	LL sum=0; LL addon=0;
	FOR(i,2,n)
	{
	    if (w[i]<w[i-1]-k)
        {
            addon=w[i-1]-k-w[i]; sum+=addon; w[i]+=addon;
            //cout << "add1 to " << i << " amount=" << addon << "\n";
        }
        else if (w[i]>w[i-1]+k)
        {
            FORD(j,i-1,1)
            {
                if (w[j]<w[j+1]-k)
                {
                    addon=w[j+1]-k-w[j]; sum+=addon; w[j]+=addon;
                    //cout << "add2 to " << j << " amount=" << addon << "\n";
                }
            }
        }
	}
	cout << sum << "\n";
	return 0;
}