#include "bits/stdc++.h"
#include <unordered_set>
#define rep(i,n) for(ll i = 0; i < n; i++)
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
#define vll vector<vector<long long>>
#define vl vector<long long>
#define vi vector<int>
#define vii vector<vector<int>>
#define pb push_back
#define pf push_front
#define ld long double
#define Sort(a) sort(a.begin(),a.end())
#define cSort(a,cmp) sort(a.begin(),a.end(),cmp)
#define reSort(a) sort(a.rbegin(), a.rend())
static const ll llMAX = numeric_limits<long long>::max();
static const int intMAX = numeric_limits<int>::max();
static const ll  llMIN = numeric_limits<long long>::min();
static const int intMIN = numeric_limits<int>::min();
static const ll d_5 = 100000;
static const ll d9_7 = 1000000007;
static const ll d_9 = 1000000000;
static const double PI=3.14159265358979323846;
template<class T>
void Printvector(std::vector<T> a){
  int size = a.size();
  rep(i,size){
    cout<<a[i]<<" ";
  }
  cout<<endl;
}
template<class T>
void Printvector(std::vector<std::vector<T>> a){
  int size = a.size();
  rep(i,size){
    int size2=a[i].size();
    rep(j,size2){
      cout<<a[i][j]<<" ";
    }
    cout<<endl;
  }
  cout<<endl;
}
ll digitpower(ll a,ll b){//aのb乗を計算
  if(b==1){
    return a;
  }else if(b==0){
    return 1;
  }
  int mode=0;
  if(b%2==1){
    ll tmp = digitpower(a,(b-1)/2);
    if(mode==1){
      tmp%=d9_7;
    }
    tmp*=tmp;
    if(mode==1){
      tmp%=d9_7;
    }
    tmp*=a;
    if(mode==1){
      return tmp%d9_7;
    }else{
      return tmp;
    }
  }else{
    ll tmp = digitpower(a,(b)/2);
    if(mode==1){
      tmp%=d9_7;
    }
    tmp*=tmp;
    if(mode==1){
      tmp%=d9_7;
    }
    if(mode==1){
      return tmp%d9_7;
    }else{
      return tmp;
    }
  }
}
vl facs(2000010,-1);
ll Factrial(ll num){
  if(facs[num]!=-1){
    return facs[num];
  }
  if(num==1||num<=0){
    return 1;
  }else if(num<0){
    printf("ERROR_minus\n");
    return 0;
  }else{
    facs[num]=(num*Factrial(num-1))%d9_7;
    return facs[num];
  }
}
long long modinv(long long a, long long m) {//modの逆元

    long long b = m, u = 1, v = 0;
    while (b) {
        long long t = a / b;
        a -= t * b; swap(a, b);
        u -= t * v; swap(u, v);
    }
    u %= m; 
    if (u < 0) u += m;
    return u;
}

vl invs(2000010,-1);
ll linercomb(ll n,ll k, ll mod){//n,kの線形時間で求める
if(n<k)return 0;
if(n<0)return 0;
if(k==0 || k==n)return 1;
  ll ans=Factrial(n);
  if(invs[k]==-1){
    invs[k]=modinv(Factrial(k),mod);
  }
  ans*=invs[k];
  ans%=d9_7;
  ll k1=Factrial(n-k);
  k1%=mod;
  ans*=modinv(k1,mod);
  ans%=mod;
  return ans;
}
unordered_map<ll,ll> prime_factor(int64_t n) {
  unordered_map<ll,ll> ret;
  for(int64_t i = 2; i * i <= n; i++) {
    while(n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if(n != 1) ret[n] = 1;
  return ret;
}

template<class T>
vector<T> getaccum(vector<T> a){
  int size=a.size();
  vector<T> ans(size);
  ans[0]=a[0];
  for(int i=0;i<size-1;i++){
    ans[i+1]=ans[i]+a[i+1];
    //ans[i+1]%=d9_7;
  }
  return ans;
}
struct datas{
  int item1;
  int item2;
  int score;
};/*
bool cmp(const datas &a, const datas &b)
{
    return a.num < b.num;
}*/
ll getaccumnum(vector<ll> accum,int l,int r){//閉区間[l,r]の総和
  if(l==0){
    return accum[r];
  }else{
    return accum[r]-accum[l-1];
  }
}

int main(void){
  int n;
  cin>>n;
  ll p;
  cin>>p;
  deque<ll> hh;
  rep(i,n){
    ll tmp;
    cin>>tmp;
    hh.pb(tmp);
  }
  rep(i,n-1){
    if(*hh.begin()>=*(++hh.begin())){
      hh.pop_front();
    }else{
      break;
    }
  }
  n=hh.size();
  vi nos(n,0);
  rep(i,n-2){
    if(hh[i]<=hh[i+1]<=hh[i+2] || hh[i]>=hh[i+1]>=hh[i+2]){
      nos[i+1]=1;
    }
  }
  deque<ll> h;
  auto now=hh.begin();
  rep(i,n){
    if(!nos[i]){
      h.push_back(*now);
    }
    now++;
  }
  n=h.size();
  ll ans=0;
  for(auto itr=h.begin();itr!=(h.end());itr++){
   // cout<<*itr<<endl;
    auto itr2=itr;
    itr2++;
    if(itr2==h.end())break;
    if(*itr<*itr2){
      ans+=min(*itr2-*itr,p);
    }
  }
  cout<<ans<<endl;
}

//<<std::setprecision(30)