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#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair < ll, ll > pii;
const ll lim = 1000'003, mod = 1e9 + 7;

ll tab[lim];

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    ll n, k;
    cin >> n >> k;
    for(int i = 1; i <= n; i++) cin >> tab[i];
    ll wyn = 0;
    for(int i = 1; i <= n; i++){
        ll w = tab[i];
        for(int j = 1; j <= n; j++){
            w = max(w, tab[j] - (abs(i - j) * k));
        }
        wyn += w - tab[i];
    }
    cout << wyn << "\n";
}