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

const int MAXN = 1006;

int h[MAXN];
bool ok[MAXN];
int n, k;

int main(){
	ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	
	priority_queue<pair<int, int>> q;
	
	cin >> n >> k;
	for(int i = 1; i <= n; i++){
		cin >> h[i];
		q.push({h[i], i});
	} 
	h[0] = h[1]; h[n+1] = h[n];
	ok[0] = true; ok[n+1] = true;
	
	int ans = 0;
	while(!q.empty()){
		auto [height, cur] = q.top();
		q.pop();
		
		if(ok[cur]) continue;//juz obsluzylismy
		
		ok[cur] = true;
		for(int i = -1; i <= 1; i += 2){//patrzymy na sasiadow
			if(!ok[cur + i]){//jest nizszy/nierozpatrzony
				if(height - h[cur + i] > k){//jest za niski
					ans += height - k - h[cur + i];
					h[cur + i] = height - k;
					q.push({h[cur + i], cur + i});
				}
			}
		}
	}
	cout << ans;
}