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#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define pb push_back
#define F first
#define S second
#define pii pair<int,int>
#define vi vector<int>
#define vpii vector<pii>

#define loop(i,n) sloop(0,i,n)
#define sloop(s, i, n) for(int i=(s);i<(n);i++)
#define rloop(i,n) rsloop(0,i,n)
#define rsloop(s,i,n) for(int i=(n);i-->(s);)

#define all(v) (v).begin(),(v).end()

#define nie {cout<<"No\n";return;}
#define tak {cout<<"Yes\n";return;}

#ifdef DEBUG
#define DBG cout << __LINE__ << endl;
#else 
#define DBG
#endif 

//int xses[8] = {-1,1,0,0,-1,1,1,-1};
//int yses[8] = {0,0,-1,1,-1,1,-1,1};

#define int ll

void solve()
{
	int n,k;
	cin>>n>>k;

	int res=0;
	vi v(n);
	loop(i,n)cin>>v[i];

	loop(i,n-1){
		int p = max(0ll,v[i]-k-v[i+1]);
		res+=p;
		v[i+1]+=p;
	}
	for(int i=n-1;i>=1;i--){
		int p = max(0ll,v[i]-k-v[i-1]);
		res+=p;
		v[i-1]+=p;
	}

	cout<<res<<'\n';


}

signed main()
{
	cin.tie(0);
	ios_base::sync_with_stdio(0);

	int t=1;


	//cin>>t;
	loop(i,t)
	{
	#ifdef DEBUG

		if(t!=1)
		{
			cout<<"Test no. "<<i+1<<endl;
		}
	#endif
	
		solve();
	}

	#ifdef DEBUG
	cout << '\n';
	#endif
	return 0;
}