#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main()
{
  std::ios::sync_with_stdio(false);
  cin.tie(NULL);
  int n, k;
  long long wyn=0, now;
  cin >> n >> k;
  int co[n];
  for (int i=0;i<n;i++)
  {
    cin >> co[i];
  }
  while (true)
  {
    now=0;
    for (int i=1;i<n;i++)
    {
      if (co[i]>co[i-1])
      {
        now+=max(0, co[i]-co[i-1]-k);
        co[i-1]=max(co[i-1], co[i]-k);
      }
      else
      {
        now+=max(0, co[i-1]-co[i]-k);
        co[i]=max(co[i], co[i-1]-k);
      }
    }
    wyn+=now;
    if (now==0)
    {
      break;
    }
  }
  cout << wyn;
}