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//fast
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;

#define all(x) x.begin(),x.end()
#define rep(n) for (int i = 0 ; i<n ; i++)
#define pb push_back

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
	int n,k;
	cin >> n >> k;
	int a[n];
	rep(n) cin >> a[i];
	ll w = 0;
	for (int i = 1 ; i<n ; i++){
		if (abs(a[i]-a[i-1])>=k){
			if (a[i]<a[i-1]){
				w+=(a[i-1]-k)-a[i];
				a[i] = a[i-1]-k;
			}else{
				for (int j = i-1 ; j>=0 ; j--){
					if (a[j+1]>a[j]+k){
						w+=a[j+1]-k-a[j];
						a[j] = a[j+1]-k;
					}
				}
			}
		}
	}
	cout << w << '\n';
}