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#include <cstdio>
#include <queue>

int N, K;
int H[1000];
bool done[1000];

int najwyzszy()
{
  int best_i = -1;
  int max_height = -1;
  for (int i=0; i<N; ++i) {
    if (!done[i] && H[i] > max_height) {
      max_height = H[i];
      best_i = i;
    }
  }
  return best_i;
}

int main()
{
  scanf("%d%d", &N, &K);

  for (int i=0; i<N; ++i) {
    scanf("%d", &H[i]);
    done[i] = false;
  }

  int zliczam = 0;

  int i0;
  while ((i0 = najwyzszy()) >= 0) {
    int min_H = H[i0] - K;
    if (i0 > 0 && H[i0-1] < min_H) {
      zliczam += min_H - H[i0-1];
      H[i0-1] = min_H;
    }
    if (i0+1 < N && H[i0+1] < min_H) {
      zliczam += min_H - H[i0+1];
      H[i0+1] = min_H;
    }
    done[i0] = true;
  }
  
  printf("%d\n", zliczam);
}