import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken().to!int; }
long readLong() { return readToken().to!long; }
real readReal() { return readToken().to!real; }

void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = cast(int)(as.length); for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a < val)); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a <= val)); }


immutable INF = 10L^^18;

int N;
long D;
long[] A;

void main() {
  try {
    for (; ; ) {
      N = readInt();
      D = readLong();
      A = new long[N];
      foreach (u; 0 .. N) {
        A[u] = readLong();
      }
      
      BinaryHeap!(Array!(Tuple!(long, int, int)), "a > b") q;
      auto dist = new long[N];
      auto ss = new int[N];
      dist[] = INF;
      ss[] = -1;
      foreach (u; 0 .. N) {
        q.insert(tuple!(long, int, int)(A[u], u, u));
      }
      for (; !q.empty; ) {
        const c = q.front[0];
        const u = q.front[1];
        const s = q.front[2];
        q.popFront;
        if (ss[u] == -1) {
          dist[u] = c;
          ss[u] = s;
          foreach (du; [+1, -1]) {
            const v = u + du;
            if (0 <= v && v < N) {
              q.insert(tuple!(long, int, int)(c + D, v, s));
            }
          }
        }
      }
      debug {
        writefln("dist = %s", dist);
        writefln("ss = %s", ss);
      }
      
      long cost(int u, int v) {
        return abs(u - v) * D + A[u] + A[v];
      }
      long ans;
      foreach (u; 0 .. N) {
        if (u != ss[u]) {
          ans += cost(u, ss[u]);
        }
      }
      foreach (u; 0 .. N - 1) {
        if (ss[u] != ss[u + 1]) {
          ans += cost(ss[u], ss[u + 1]);
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}
