#include <bits/stdc++.h>

using namespace std;

typedef long long int64;
const int64 INF = 1LL << 59;

int main()
{
  int N, P, H[200000];

  cin >> N >> P;
  for(int i = 0; i < N; i++) cin >> H[i];

  int64 dp1[200001], dp2[200001];
  dp1[0] = 0;
  dp2[0] = INF;
  for(int i = 0; i + 1 < N; i++) {
    dp1[i + 1] = min(dp1[i] + max(0, H[i + 1] - H[i]), min(dp1[i], dp2[i]) + P);
    dp2[i + 1] = min(dp2[i] + max(0, H[i] - H[i + 1]), min(dp1[i], dp2[i]) + P);
  }
  cout << min(dp1[N - 1], dp2[N - 1]) << endl;
}