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/* 
 * Author: KarolB
 * Time: 2026-03-25 11:35:12
**/

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

typedef long long ll;


constexpr int MAXN = 1e3+6;
int a[MAXN];

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  for(int i = 1; i <= n; i++ ){
    cin >> a[i];
  }
  ll res = 0;
  for(int pt = 0; pt < 2; pt++){
    for(int i = 2; i <= n; i++){
      if(a[i-1] - a[i] > k){
        res += (a[i-1] - a[i]-k);
        a[i] += (a[i-1] - a[i]-k);
      }
    }
    reverse(a+1, a+n+1);
  }
  cout << res << '\n';
  return 0;
}