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#include <bits/stdc++.h>
using namespace std;

using ll = int64_t;

constexpr ll mod = 1000000007;

void solve() {
  int n, k;
  cin >> n >> k;

  vector<int> vs(n);  
  for(auto& v : vs) {
    cin >> v;
  }

  vector<int> m = vs;
  for(int i = 0; i < n; i++) {
    for(int j = 0; j < n; j++) {
      int dist = abs(j - i);
      int need = vs[i] - dist * k;
      m[j] = max(m[j], need);
    }
  }

  int ans = 0;
  for(int i = 0; i < n; i++) {
    ans += m[i] - vs[i];
  }

  cout << ans;
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  //freopen("in", "r", stdin);
  solve();
}