//#define __USE_MINGW_ANSI_STDIO 0
#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
#define int ll
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define IN(a, b, x) (a<=x&&x<b)
#define MP make_pair
#define PB push_back
#ifdef int
const ll INF = (1LL<<60);
#else
const int INF = (1LL<<30);
#endif
const double PI = 3.14159265359;
const double EPS = 1e-12;
const int MOD = 1000000007;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

int h[200010];
signed main(void)
{
  int n, p;
  cin >> n >> p;
  REP(i, n) cin >> h[i];

  int now = 0, ret = 0;
  bool flag = false;
  while(now < n) {
    int res = 0;
    while(now < n-1 && h[now] <= h[now+1]) {
      // cout << h[now+1]-h[now] << endl;
      res += max(0LL, h[now+1]-h[now]);
      now++;
    }
    ret += min(res, p*2);
    if(res > p*2) flag = true;
    else flag = false;
    // cout << now << " " << ret << endl;
    now++;
  }
  if(flag) ret -= p;
  cout << ret << endl;

  return 0;
}