#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;
  dp[0][1] = 0;
  int prev = 0;
  rep(i,N-1){
    if(H[i] > H[i+1]){
      dp[i+1][0] = min(dp[i+1][0], dp[i][1] + P);
      dp[i+1][0] = min(dp[i+1][0], dp[i][0]);
      prev = i+1;
    }else{
      dp[i+1][0] = min(dp[i+1][0], dp[i][0] + H[i+1]-H[i]);
      dp[i+1][0] = min(dp[i+1][0], dp[i][0] + P);
      dp[i+1][1] = min(dp[i+1][1], dp[prev][0] + P);
    }
  }

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