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

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vll = vector<ll>;

#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)(x).size()
#define pb push_back
#define ff first
#define ss second

const int INF = 1e9;
const ll LINF = 1e18;

void solve() {
  int n, k;

  cin >> n >> k;
  vi v(n);
  if (n == 1) {
    cout << 0 << endl;
    return;
  }

  /* cerr << "Test: " << "n: " << n << " k: " << k << endl; */
  for (auto &i : v) {
    cin >> i;
  }

  // for (auto i : v) {
  //   cout << i << " ";
  // }
  // cout << endl;

  int res = 0;
  for (int i = 1; i < n; i++) {
    int prev = v[i - 1];
    int current = v[i];

    int diff = abs(current - prev);
    int toAdd = 0;
    if (diff > k) {
      toAdd = diff - k;
    }

    if (prev < current) {
      v[i - 1] = prev + toAdd;
    } else if (current < prev) {
      v[i] = current + toAdd;
    }
    res += toAdd;
  }

  for (int i = n - 2; i >= 0; i--) {
    int prev = v[i + 1];
    int current = v[i];

    int diff = abs(current - prev);
    int toAdd = 0;
    if (diff > k) {
      toAdd = diff - k;
    }

    // cout << "prev: " << prev << " current: " << current << " diff: " << diff
    //      << endl;

    if (prev < current) {
      v[i + 1] = prev + toAdd;
    } else if (current < prev) {
      v[i] = current + toAdd;
    }
    res += toAdd;
  }

  // for (auto i : v) {
  //   cout << i << " ";
  // }

  cout << res << endl;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(0);

  int t = 1;
  while (t--)
    solve();

  return 0;
}