#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define REPS(i,x) for(int i=1;i<=(int)(x);i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RREPS(i,x) for(int i=((int)(x));i>0;i--)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) (container).begin(), (container).end()
#define RALL(container) (container).rbegin(), (container).rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define pb push_back
#define eb emplace_back
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define __builtin_popcount __builtin_popcountll

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
    os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
    os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const map<S, T> &t) {
    os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T> pair<S,T> operator+(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first+t.first, s.second+t.second);}
template<class S, class T> pair<S,T> operator-(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first-t.first, s.second-t.second);}

const int INF = 1<<28;
const double EPS = 1e-8;
const int MOD = 1000000007;

struct UnionFind {
    vector<int> d;
    UnionFind(int n=0) : d(n, -1){}
    bool unite(int x, int y) {
        if ((x = root(x)) != (y = root(y))){
            if (d[y] < d[x]) swap(x, y);
            d[x] += d[y]; d[y] = x;
        }
        return x != y;
    }
    bool find(int x, int y){return root(x) == root(y);}
    int root(int x){return d[x] < 0 ? x : d[x] = root(d[x]);}
    int size(int x=-1) {return x<0 ? d.size() : -d[root(x)];}
};


ll T, n, m;

int main(int argc, char *argv[]){
    ios::sync_with_stdio(false);
    while(cin >> n >> m){
        vector<ll> v(n);
        REP(i, n) cin >> v[i];
        priority_queue<pll, vector<pll>, greater<pll>> pq;
        UnionFind uf(n);
        REP(i, n) {
            pq.emplace(v[i], i);
        }
        ll ans = 0;
        while(!pq.empty()) {
            ll a; int i; tie(a, i) = pq.top(); pq.pop();
            for (int j : {i - 1, i + 1}) {
                if (0 <= j && j < n && !uf.find(i, j)) {
                    uf.unite(i, j);
                    ans += a + v[j] + m;
                    if (chmin(v[j], a + m)) {
                        pq.emplace(a + m, j);
                    }
                }
            }
        }
        cout << ans << endl;
    }
    return 0;
}


Measured memory_bytes: 8816