//#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], dp[2][200010];
signed main(void)
{
  int n, p;
  cin >> n >> p;
  REP(i, n) cin >> h[i];

  REP(i, 2) REP(j, n) dp[i][j] = INF;
  dp[0][0] = 0;

  FOR(i, 1, n) {
    dp[0][i] = min(min(dp[0][i-1], dp[1][i-1])+p, dp[0][i-1] + max(0LL, h[i]-h[i-1]));
    dp[1][i] = min(min(dp[0][i-1], dp[1][i-1])+p, dp[1][i-1] + max(h[i-1]-h[i], 0LL));
  }

  // REP(i, 2) {
  //   REP(j, n) cout << dp[i][j] << " ";
  //   cout << endl;
  // }

  cout << min(dp[0][n-1], dp[1][n-1]) << endl;

  return 0;
}