#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ld = long double;
const int INF = (int)1e9+5;
void solve(){
  int n, h;
  cin >> n >> h;

  vector<ll> a(n);
  for(ll& x: a)cin >> x;
  if (!h)
    return void(cout << 0);

  vector<ll> dp(n+1, INF);
  dp[0] = 0;
  for(int i = 0; i < n; i++){
    for(int j = i; j >= 0; j--){
      ll dis = a[i] - a[j]; // 3 - 14 = 12/2 = 6 [2 3] [7 8]
      if (i == j)
        dis = 2;
      ll bricks = (dis+1)/2;
      if (bricks > h)continue;

      ll total = bricks * (bricks - 1)/2 + (h - bricks) + 1 - max((2 * (bricks - 3) - 1), 0LL);
      
      bool alone = true;
      for(int k = j+1; k <= i; k++){
        if (!alone){
          alone = true;
          total++;
        }else{
          if (a[k]-(a[k-1]+1) <= 1)
            alone = false;
          else total++;
        }
      }

      // if (i == n-1)
      //   cout << dp[j] <<  ' ' << dp[i+1] << ' ' << total << ' ' << bricks <<  endl;
      dp[i+1] = min(dp[i+1], dp[j] + total);
    }
  }
  cout << dp[n];
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout << fixed << setprecision(6);

  int t = 1;
  // cin >> t;

  while(t--){
    solve();
    cout << '\n';
  }

  return 0;
}