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

typedef long long   signed int LL;
typedef long long unsigned int LU;

#define incID(i, l, r) for(int i = (l)    ; i <  (r); i++)
#define incII(i, l, r) for(int i = (l)    ; i <= (r); i++)
#define decID(i, l, r) for(int i = (r) - 1; i >= (l); i--)
#define decII(i, l, r) for(int i = (r)    ; i >= (l); i--)
#define  inc(i, n) incID(i, 0, n)
#define inc1(i, n) incII(i, 1, n)
#define  dec(i, n) decID(i, 0, n)
#define dec1(i, n) decII(i, 1, n)

#define inII(v, l, r) ((l) <= (v) && (v) <= (r))
#define inID(v, l, r) ((l) <= (v) && (v) <  (r))

#define PB push_back
#define EB emplace_back
#define MP make_pair
#define FI first
#define SE second
#define PQ priority_queue

#define  ALL(v)  v.begin(),  v.end()
#define RALL(v) v.rbegin(), v.rend()
#define  FOR(it, v) for(auto it =  v.begin(); it !=  v.end(); ++it)
#define RFOR(it, v) for(auto it = v.rbegin(); it != v.rend(); ++it)

template<typename T> bool   setmin(T & a, T b) { if(b <  a) { a = b; return true; } else { return false; } }
template<typename T> bool   setmax(T & a, T b) { if(b >  a) { a = b; return true; } else { return false; } }
template<typename T> bool setmineq(T & a, T b) { if(b <= a) { a = b; return true; } else { return false; } }
template<typename T> bool setmaxeq(T & a, T b) { if(b >= a) { a = b; return true; } else { return false; } }
template<typename T> T gcd(T a, T b) { return (b == 0 ? a : gcd(b, a % b)); }
template<typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }

// ---- ----

template<typename T> class SegmentTree {
private:
	T * a = NULL;
	int N = -1, S;
	function<T(T, T)> F;
	T I;
	bool is_available = false;
public:
	SegmentTree() { }
	SegmentTree(int n, function<T(T, T)> func, T id) { init(n, func, id); }
	void init(int size, function<T(T, T)> func, T id) {
		assert(size > 0);
		N = size;
		F = func;
		I = id;
		S = 1;
		while(S < size) { S *= 2; }
		delete[] a;
		a = new T[S * 2];
		inc(i, S * 2) { a[i] = I; }
		is_available = true;
	}
	const T & operator[](int p) {
		assert(inID(p, 0, N));
		p += S;
		return a[p];
	}
	T & ref(int p) {
		is_available = false;
		assert(inID(p, 0, N));
		p += S;
		return a[p];
	}
	void calc() {
		decID(i, 1, S) { a[i] = F(a[i * 2], a[i * 2 + 1]); }
		is_available = true;
	}
	void apply(int p, function<void(T &)> op) {
		assert(inID(p, 0, N));
		p += S;
		op(a[p]);
		while(p != 1) {
			p /= 2;
			a[p] = F(a[p * 2], a[p * 2 + 1]);
		}
	}
	T fold_ID(int l, int r, bool loop = false) {
		assert(is_available);
		assert(inII(l, 0, N));
		assert(inII(r, 0, N));
		if(loop && l >= r) { return F(fold_ID(l, N), fold_ID(0, r)); }
		assert(l <= r);
		l += S;
		r += S;
		T v = I, w = I;
		while(l < r) {
			if(l + 1 == r) { v = F(v, a[l]); break; }
			if(l % 2 == 1) { v = F(v, a[l]); }
			if(r % 2 == 1) { w = F(a[r - 1], w); }
			l = (l + 1) / 2;
			r = r / 2;
		}
		return F(v, w);
	}
	T fold_II(int l, int r, bool loop = false) { return fold_ID(l    , r + 1, loop); }
	T fold_CD(int l, int r, bool loop = false) { return fold_ID(l + 1, r    , loop); }
	T fold_CI(int l, int r, bool loop = false) { return fold_ID(l + 1, r + 1, loop); }
};

#define OP(op) [&](auto A, auto B) { return op; }
#define AP(op) [&](auto & A) { op; }

// ---- ----

LL n, d, a[200000], INF = 1e18;
SegmentTree<pair<LL, int>> st[2];
SegmentTree<pair<LL, pair<int, int>>> ST;

void sf(int i) {
	inc(k, 2) { st[k].apply(i, AP(A = MP(INF, -1))); }
}

auto ch(int i) {
	auto x = st[0].fold_ID(0, i);
	auto y = st[1].fold_CD(i, n);
	
	auto X = MP(x.FI + a[i] - (n - 1 - i) * d, MP(i, x.SE));
	auto Y = MP(y.FI + a[i] -          i  * d, MP(i, y.SE));
	auto Z = min(X, Y);
	
	ST.apply(i, AP(A = Z));
	
	return Z;
}

int main() {
	cin >> n >> d;
	inc(i, n) { cin >> a[i]; }
	
	inc(k, 2) { st[k].init(n, OP(min(A, B)), MP(INF, 0)); }
	inc(i, n) { st[0].ref(i) = MP((n - 1 - i) * d + a[i], i); }
	inc(i, n) { st[1].ref(i) = MP(         i  * d + a[i], i); }
	inc(k, 2) { st[k].calc(); }
	
	ST.init(n, OP(min(A, B)), MP(INF, MP(0, 0)));
	
	LL ans = 0;
	sf(0);
	ch(0);
	inc(i, n - 1) {
		LL s;
		int x, y;
		while(true) {
			auto mi = ST.fold_ID(0, n);
			s = mi.FI;
			x = mi.SE.FI;
			y = mi.SE.SE;
			ch(x);
			auto mi2 = ST.fold_ID(0, n);
			if(mi == mi2) { break; }
		}
		ans += s;
		
		sf(x);
		sf(y);
		ch(x);
		ch(y);
	}
	
	cout << ans << endl;
	
	return 0;
}
