#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

#define INF 9222222222222222222LL

ll dp[200005][2];

int main(){
  int N;
  ll P;
  vector<ll> H;
  cin >> N >> P;
  rep(i,N){
    ll a;
    cin >> a;
    H.push_back(a);
  }

  rep(i,200005){
    dp[i][0] = INF;
    dp[i][1] = INF;
  }
  dp[0][0] = 0;
  REP(i,1,N){
    //i-1  i
    // -> & ->
    dp[i][0] = min(dp[i][0], dp[i-1][0] + max(0LL,H[i]-H[i-1]));
    dp[i][0] = min(dp[i][0], dp[i-1][0] + P);

    // -> & <-
    dp[i][1] = min(dp[i][1], dp[i-1][0] + P);

    // <- & ->
    dp[i][0] = min(dp[i][0], dp[i-1][1] + P);

    // <- & <-
    dp[i][1] = min(dp[i][1], dp[i-1][1] + max(0LL,H[i-1]-H[i]));
    dp[i][1] = min(dp[i][1], dp[i-1][1] + P);
  }


  cout << min(dp[N-1][0], dp[N-1][1]) << endl;
  
  return 0;
}