#include <bits/stdc++.h>
#define REP(i, a, n) for(ll i = ((ll) a); i < ((ll) n); i++)
#define INF (1LL << 60)
using namespace std;
typedef long long ll;

ll N, P, H[200000];

int main(void) {
  cin >> N >> P;
  REP(i, 0, N) cin >> H[i];

  vector<ll> dp1(N), dp2(N);
  dp1[0] = 0;
  dp2[0] = INF;
  REP(i, 1, N) {
    dp1[i] = min(min(dp1[i - 1], dp2[i - 1]) + P, dp1[i - 1] + max(H[i] - H[i - 1], 0LL));
    dp2[i] = min(min(dp1[i - 1], dp2[i - 1]) + P, dp2[i - 1] + max(H[i - 1] - H[i], 0LL));
  }
  cout << min(dp1[N - 1], dp2[N - 1]) << endl;
}