import java.io.*;
import java.util.*;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.IntFunction;

public class Main {

    static int N, D;
    static int[] A;

    public static void main(String[] args) {
        FastScanner sc = new FastScanner(System.in);
        N = sc.nextInt();
        D = sc.nextInt();
        A = sc.nextIntArray(N);

        System.out.println(solve());
    }

    static City INF = new City(-1, Long.MAX_VALUE);

    static long solve() {
        // プリム法っぽいやりかた
        // 現在結合されている都市から生えている道の中から一番安いものを利用してつなげていく
        BinaryOperator<City> merge = (a, b) -> a.cost < b.cost ? a : b;

        RangeGetObj<City> lseg = new RangeGetObj<>(N, INF, merge, City[]::new);
        for (int i = 0; i < N; i++) {
            long cost = D * (N-i-1) + A[i];
            lseg.update(i, new City(i, cost));
        }
        RangeGetObj<City> rseg = new RangeGetObj<>(N, INF, merge, City[]::new);
        for (int i = 0; i < N; i++) {
            long cost = D * i + A[i];
            rseg.update(i, new City(i, cost));
        }
        UnionFind uf = new UnionFind(N);
        PriorityQueue<Road> q = new PriorityQueue<>(Comparator.comparingLong(r -> r.cost));

        // 0から開始
        City near0 = rseg.query(1, N);
        Road r0 = new Road(0, near0.i, cost(0, near0.i));
        q.add( r0 );
        lseg.update(0, INF);
        rseg.update(0, INF);

        long ans = 0;
        int cnt = 1;
        while(true) {
            Road road = q.poll();
            if( !uf.isSame(road.from, road.to) ) {
                uf.unite(road.from, road.to);
                ans += road.cost;

                // toはもう不要
                lseg.update(road.to, INF);
                rseg.update(road.to, INF);
                cnt++;
                if( cnt == N ) break;

                // from, toからの最小を追加する
                q.add( cheapest(road.from, lseg, rseg) );
                q.add( cheapest(road.to, lseg, rseg) );

            } else {
                // roadがダメだったのでfromから次のやつを持ってくる
                q.add( cheapest(road.from, lseg, rseg) );
            }
        }
        return ans;
    }

    static Road cheapest(int i, RangeGetObj<City> lseg, RangeGetObj<City> rseg) {
        City lCity = lseg.query(0, i);
        City rCity = rseg.query(i+1, N);

        Road lRoad = lCity == INF ? null : new Road(i, lCity.i, cost(i, lCity.i));
        Road rRoad = rCity == INF ? null : new Road(i, rCity.i, cost(i, rCity.i));

        if( lRoad != null && rRoad != null ) {
            return lRoad.cost < rRoad.cost ? lRoad : rRoad;
        } else if( lRoad != null ) {
            return lRoad;
        } else {
            return rRoad;
        }
    }

    static long cost(int a, int b) {
        return (long)A[a] + A[b] + (long)Math.abs(a-b) * D;
    }

    static class City {
        int i;
        long cost;

        public City(int i, long cost) {
            this.i = i;
            this.cost = cost;
        }

        public String toString() {
            return "City(" + i + ", " + cost + ")";
        }
    }

    static class Road {
        int from, to;
        long cost;

        public Road(int from, int to, long cost) {
            this.from = from;
            this.to = to;
            this.cost = cost;
        }
    }

    static class RangeGetObj<A> {

        int size;
        A[] tree;
        A identity;
        BinaryOperator<A> merge;

        RangeGetObj(int size, A identity, BinaryOperator<A> merge, IntFunction<A[]> mkArr) {
            this.size = 1;
            while( this.size < size ) this.size *= 2;
            this.tree = mkArr.apply(this.size*2);
            this.identity = identity;
            this.merge = merge;
            Arrays.fill(tree, identity);
        }

        void update(int idx, A a) {
            idx += size;
            tree[idx] = a;

            while(idx > 0) {
                idx /= 2;
                tree[idx] = merge.apply(tree[idx*2], tree[idx*2+1]);
            }
        }

        // [from, to)
        A query(int from, int to) {
            return _query(from, to, 1, 0, size);
        }

        private A _query(int from, int to, int idx, int l, int r) {
            if (r <= from || to <= l) return identity;

            if (from <= l && r <= to) {
                return tree[idx];

            } else {
                int mid = (l+r)/2;
                A vl = _query(from, to, idx*2, l, mid);
                A vr = _query(from, to, idx*2+1, mid, r);
                return merge.apply(vl, vr);
            }
        }

        A get(int idx) {
            return tree[idx+size];
        }
    }

    static class UnionFind {

        private final int[] parent;
        private final int[] rank;

        public UnionFind(int n) {
            parent = new int[n];
            rank = new int[n];
            for (int i = 0; i < n; i++) {
                parent[i] = i;
                rank[i] = 0;
            }
        }

        public int root(int i) {
            if( parent[i] == i ) {
                return i;
            } else {
                return parent[i] = root(parent[i]);
            }
        }

        public int unite(int i, int j) {
            int ri = root(i);
            int rj = root(j);
            if( ri == rj ) return ri;

            if( rank[ri] < rank[rj] ) {
                parent[ri] = rj;
                return rj;

            } else {
                parent[rj] = ri;
                if( rank[ri] == rank[rj] ) {
                    rank[ri]++;
                }
                return ri;
            }
        }

        public boolean isSame(int a, int b) {
            return root(a) == root(b);
        }
    }

    @SuppressWarnings("unused")
    static class FastScanner {
        private BufferedReader reader;
        private StringTokenizer tokenizer;

        FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken("\n");
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        int[] nextIntArray(int n, int delta) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt() + delta;
            return a;
        }

        long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

    static <A> void writeLines(A[] as, Function<A, String> f) {
        PrintWriter pw = new PrintWriter(System.out);
        for (A a : as) {
            pw.println(f.apply(a));
        }
        pw.flush();
    }

    static void writeLines(int[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (int a : as) pw.println(a);
        pw.flush();
    }

    static void writeLines(long[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (long a : as) pw.println(a);
        pw.flush();
    }

    static int max(int... as) {
        int max = Integer.MIN_VALUE;
        for (int a : as) max = Math.max(a, max);
        return max;
    }

    static int min(int... as) {
        int min = Integer.MAX_VALUE;
        for (int a : as) min = Math.min(a, min);
        return min;
    }

    static void debug(Object... args) {
        StringJoiner j = new StringJoiner(" ");
        for (Object arg : args) {
            if (arg instanceof int[]) j.add(Arrays.toString((int[]) arg));
            else if (arg instanceof long[]) j.add(Arrays.toString((long[]) arg));
            else if (arg instanceof double[]) j.add(Arrays.toString((double[]) arg));
            else if (arg instanceof Object[]) j.add(Arrays.toString((Object[]) arg));
            else j.add(arg.toString());
        }
        System.err.println(j.toString());
    }
}
