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#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef double db;
typedef pair<int, int> pii;
#define all(x) (x).begin(), (x).end()
#define sz(x) (x).size()
#define rep(i, l, r) for(int i=l; i<(r); i++)

void solve(){
    ll n, k;
    cin >> n >> k;
    vector<ll> a(n);
    for(auto &e : a) cin >> e;
    ll ans = 0;
    rep(i, 0, n) {
        ll ile = 0;
        rep(j, 0, n) {
            ile = max(ile, a[j]-k*abs(i-j)-a[i]);
        }
        ans += ile;
    }
    cout << ans << "\n";
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
    while(t--){
        solve();
    }
}