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#include <bits/stdc++.h>
#pragma GCC target ("avx2,fma")
#pragma GCC optimize ("Ofast")
#pragma GCC optimize ("unroll-loops")

#define int long long
#define ll long long
#define ld long double
#define endl '\n'
#define st first
#define nd second
#define pb push_back
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define FOR(i,l,r) for(int i=(l);i<=(r);i++)
#define ROF(i,r,l) for(int i=(r);i>=(l);i--)
using namespace std;
ll inf=1000000000000000007;
const int mod=1000000007;
int mod1=998244353;

#ifdef LOCAL
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif

const int N=1007;

int a[N],b[N];

signed main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
	int n,k;
	cin>>n>>k;
	FOR(i,1,n) cin>>a[i];
	FOR(i,1,n) FOR(j,1,n) b[j]=max(b[j],a[i]-abs(i-j)*k);
	int ans=0;
	FOR(i,1,n) ans+=b[i]-a[i];
	cout<<ans<<endl;
    return 0;
}