
#include <bits/stdc++.h>

#define ln                 '\n'
#define all(dat)           dat.begin(), dat.end()
#define loop(i, to)        for (int i = 0; i < to; ++i)
#define cont(i, to)        for (int i = 1; i <= to; ++i)
#define circ(i, fm, to)    for (int i = fm; i <= to; ++i)
#define foreach(i, dat)    for (__typeof(dat.begin()) i = dat.begin(); i != dat.end(); ++i)

typedef long long          num;

using namespace std;

const int nsz = 2e5;
const num inf = 0x3f3f3f3f3f3f3f3f;
int n, l[nsz + 5], r[nsz + 5];
num d, a[nsz + 5], ans;

num inline w1(int id) {
	return a[id] - d * id;
}

num inline w2(int id) {
	return a[id] + d * id;
}

num inline w(int u, int v) {
	return a[u] + a[v] + d * abs(u - v);
}

int main() {
	scanf("%d%lld", &n, &d);
	cont (i, n) {
		scanf("%lld", &a[i]);
	}
	a[0] = inf, a[n + 1] = inf;
	cont (i, n) {
		l[i] = w1(l[i - 1]) < w1(i) ? l[i - 1] : i;
	}
	for (int i = n; i >= 1; --i) {
		r[i] = w2(r[i + 1]) < w2(i) ? r[i + 1] : i;
	}
	int pre = 0;
	cont (i, n) {
		if (l[i] == i && r[i] == i) {
			if (pre)  ans += w(pre, i);
			pre = i;
		} else {
			ans += min(l[i] != i ? w(l[i], i) : inf, r[i] != i ? w(i, r[i]) : inf);
		}
	}
	cout << ans << ln;
}