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#include <bits/stdc++.h>

using namespace std;
int k,n,q,i,j,b,u,L,R,g,e,f,jj;
long long m,z,xx,w;
priority_queue<array<int,2>> a;
vector<bool> v;
vector<int> h;

int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	m=1e9+7;
	cin >> n >> k;
	for(i=0;i<n;i++){
		cin >> b;
		a.push({b,i});
		h.push_back(b);
		v.push_back(0);
	}
	z=0;
	while(!a.empty()) {
		g=a.top()[0];
		e=a.top()[1];
		a.pop();
		if(v[e]) continue;
		v[e]=1;
		if (e>0 and !v[e-1] and h[e-1]<g-k)
		{
			z+=g-k-h[e-1];
			h[e-1]=g-k;
			a.push({g-k,e-1});
		}
		if (e<n-1 and !v[e+1] and h[e+1]<g-k)
		{
			z+=g-k-h[e+1];
			h[e+1]=g-k;
			a.push({g-k,e+1});
		}
	}
	cout << z << '\n';
}