// Code By H~S~C
#ifdef ONLINE_JUDGE
#pragma GCC optimize(1)
#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize(4)
#pragma comment(linker, "/STACK:1024000000,1024000000")
#pragma GCC optimize("Os")
#pragma GCC optimize("Og")
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,sse,sse2,sse3,ssse3,sse4")
#endif
#include <initializer_list>
#include <unordered_set>
#include <unordered_map>
#include <algorithm>
#include <iostream>
#include <utility>
#include <cstdlib>
#include <cstring>
#include <vector>
#include <cstdio>
#include <queue>
#include <stack>
#include <cmath>
#include <map>
#include <set>
#define pb push_back
#define rep(i,n) for (int i=0;i<(n);++i)
#define rep1(i,n) for (int i=1;i<=(n);++i)
#define Rep(i,a,b) for (int i=(a);i<=(b);++i)
#define All(a) a.begin(),a.end()
#define SZ(a) ((int)a.size())
#define sqr(s) ((s)*(s))
#define MP make_pair
#define fillset(a,val) memset(a,val,sizeof(a))
#define X first
#define Y second
#define endl '\n'
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair <int,int> pii;
const int inf=0x3f3f3f3f;
const ll lnf=0x3f3f3f3f3f3f3f3f;
const double EPS=1e-9,PI=acos(-1.0);
const int mod1=1000000007,mod2=998244353;
//....................密..........封..........线..........下..........禁..........止..........hack...............................................
const int Maxn=200005;
ll n,d,a[Maxn],dpl[Maxn],dpr[Maxn],ans;
signed main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(nullptr);cout.tie(nullptr);
	cin>>n>>d;rep(i,n) cin>>a[i],ans+=a[i];
	ans+=(n-1)*d;dpl[0]=a[0];dpr[n-1]=a[n-1];
	rep1(i,n-1) dpl[i]=min(a[i],dpl[i-1]+d);
	for (int i=n-2;~i;--i) dpr[i]=min(a[i],dpr[i+1]+d);
	rep1(i,n-2) ans+=min(dpl[i],dpr[i]);
	cout<<ans<<endl;
	return 0;
}