#include<bits/stdc++.h>
using namespace std;
#define int long long

const int INF = 1 << 30;

signed main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n,p; cin >> n >> p;
  vector<int> h(n);
  for(int i = 0; i < n; i++){
    cin >> h[i];
  }

  vector<int> dp1(n,INF); //右向きの遷移
  vector<int> dp2(n,INF); //左向きの遷移
  dp1[0] = 0;
  dp2[0] = INF;
  for(int i = 0; i < n-1; i++){
    dp1[i+1] = min(dp1[i]+max(0LL,h[i+1]-h[i]), min(dp1[i],dp2[i])+p);
    dp2[i+1] = min(dp2[i]+max(0LL,h[i]-h[i+1]), min(dp1[i],dp2[i])+p);
  }
  cout << min(dp1[n-1],dp2[n-1]) << endl;

  return 0;
}