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#include<bits/stdc++.h>

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define VAR(v, i) __typeof(i) v=(i)
#define FORE(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)


#define VI vector<int>
#define PII pair<int,int>
#define st first
#define nd second
#define mp make_pair
#define pb push_back
#define lint long long int


#define debug(x) {cerr <<#x <<" = " <<x <<endl; }
#define debug2(x,y) {cerr <<#x <<" = " <<x << ", "<<#y<<" = "<< y <<endl; }
#define debug3(x,y,z) {cerr <<#x <<" = " <<x << ", "<<#y<<" = "<< y << ", " << #z << " = " << z <<endl; }
#define debugv(x) {{cerr <<#x <<" = "; FORE(itt, (x)) cerr <<*itt <<", "; cerr <<endl; }}
#define debugt(t,n) {{cerr <<#t <<" = "; FOR(it,0,(n)) cerr <<t[it] <<", "; cerr <<endl; }}


#define make( x) int (x); scanf("%d",&(x));
#define make2( x, y) int (x), (y); scanf("%d%d",&(x),&(y));
#define make3(x, y, z) int (x), (y), (z); scanf("%d%d%d",&(x),&(y),&(z));
#define make4(x, y, z, t) int (x), (y), (z), (t); scanf("%d%d%d%d",&(x),&(y),&(z),&(t));
#define IOS ios_base::sync_with_stdio(0)
#define HEAP priority_queue


#define read( x) scanf("%d",&(x));
#define read2( x, y) scanf("%d%d",&(x),&(y));
#define read3(x, y, z) scanf("%d%d%d",&(x),&(y),&(z));
#define read4(x, y, z, t) scanf("%d%d%d%d",&(x),&(y),&(z),&(t));


using namespace std;

int juz[1005];
int fin[1005];
int v[1005];

int main() {
	make2(n, k);
	FOR(i,0,n) {
		make(a); 
		fin[i] = v[i] = a;
		juz[i] = 0;
	}
	
	FOR(rep,0,n) {
		int best = 0;
		int dla = 0;
		FOR(j,0,n) {
			if (juz[j]) continue;
			best = max(best, fin[j]);
			if (best == fin[j]) dla = j;
		}
		juz[dla] = 1;
		FOR(j,0,n) fin[j] = max(fin[j], fin[dla]-abs(dla-j)*k); 
	}
	lint total = 0;
	FOR(i,0,n) {
		total += fin[i] - v[i];
	}
	printf("%lld\n", total);
}