/**
* code generated by JHelper
* More info: https://github.com/AlexeyDmitriev/JHelper
* @author win11905
*/
#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
#define vi vector<int>
#define iii tuple<int, int, int>
#define long long long
#define pii pair<int, int>
#define x first
#define y second
using namespace std;
const long MOD = 1e9+7, LINF = 1e18 + 1e16;
const int INF = 1e9+1;
const double EPS = 1e-10;
const int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
const int N = 2e5+5;
class safety {
private:
int n;
long k, high, now;
multiset<long> Sl, Sr;
public:
void solve(istream& cin, ostream& cout) {
cin >> n >> k;
for(int i = 0; i < n; ++i) {
cin >> now;
high += now;
Sl.emplace(now + i*k), Sr.emplace(now - i*k);
while(*Sl.rbegin() - i*k > *Sr.begin() + i*k) {
long a = *Sl.rbegin(), b = *Sr.begin();
Sl.erase(Sl.find(*Sl.rbegin())), Sr.erase(Sr.find(*Sr.begin()));
Sl.emplace(b + 2*i*k), Sr.emplace(a - 2*i*k);
}
long pv = 0;
while(!Sl.empty() && *Sl.begin() - i*k <= k) {
high -= Sl.size() * (*Sl.begin() - i*k - pv);
pv = *Sl.begin() - i*k;
Sl.erase(Sl.begin());
}
high -= Sl.size() * (k - pv);
}
long pv = 0, ptr = Sl.size();
for(auto x : Sl) {
high -= ptr-- * (x - n*k - pv);
pv = x - n*k;
}
cout << high << endl;
}
};
class Solver {
public:
void solve(std::istream& in, std::ostream& out) {
safety *obj = new safety();
obj->solve(in, out);
}
};
int32_t main() {
ios::sync_with_stdio(false);
cin.tie(0);
Solver solver;
std::istream& in(std::cin);
std::ostream& out(std::cout);
solver.solve(in, out);
return 0;
}
