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#include <bits/stdc++.h>

using namespace std;
#define pb push_back
#define st first
#define nd second
typedef long long ll;
typedef long double ld;

const ll I = 1'000'000'000'000'000'000LL;
const int II = 2'000'000'000;
const ll M = 1'000'000'007LL;
const int N = 1<<19;
ll tab[N];

void Solve()
{
    int n; ll k;
    cin >> n >> k;
    for(int i = 1; i <= n; ++i)
        cin >> tab[i];
    ll ans = 0LL;
    for(int i = 1; i <= n; ++i)
        for(int j = 1; j <= n; ++j)
        {
            ll d = abs(j - i);
            ans += max(0LL, tab[j] - k * d - tab[i]);
            tab[i] = max(tab[i], tab[j] - k * d);
        }
    cout << ans << "\n";
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    //int t; cin >> t;
    //while(t--)
        Solve();

    return 0;
}