#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <string>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <stdio.h>
using namespace std;
#define int long long
int MOD = 1000000007;
int INF = (int)1 << 60;
signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int N, P;
	cin >> N >> P;

	vector<int> A(N);
	int res = 0;
	for (int i = 0; i < N; i++) {
		cin >> A[i];
	}

	A.erase(unique(A.begin(), A.end()), A.end());
	vector<int> dp0(N, (int)1 << 60);
	vector<int> dp1(N, (int)1 << 60);
	vector<int> dp2(N, (int)1 << 60);
	vector<int> dp3(N, (int)1 << 60);
	int ne = 0;
	int ne2 = 0;
	N = A.size();
	if (N == 1) {
		cout << 0 << endl;
		return 0;
	}
	else {
		for (int i = 0; i < N; i++) {
			if (i == N - 1) {
				dp0[i] = min(dp2[i - 1], dp3[i - 1]) + P + min(P, max((int)0, A[i - 1] - A[i]));
				dp1[i] = min(dp1[i], min(dp0[i - 1], dp1[i - 1])) + min(P, max((int)0, A[i] - A[i - 1]));
				//dp2[i] = min(dp2[i], min(dp0[i - 1], dp2[i - 1])) + max((int)0, A[i - 1] - A[i]);

			}
			else if (i == 0) {
				dp0[0] = 0;
				dp1[0] = 0;
				dp2[0] = 0;
				dp3[0] = 0;
			}
			else {
				dp0[i] = min(dp2[i - 1], dp3[i - 1]) + 2 * P + min(P, max((int)0, A[i - 1] - A[i]));
				dp1[i] = min(dp0[i - 1], dp1[i - 1]) + min(P, max((int)0, A[i] - A[i - 1]));
				dp2[i] = min(dp3[i - 1], dp2[i - 1]) + min(P, max((int)0, A[i - 1] - A[i]));
				dp3[i] = min(dp1[i - 1], dp0[i - 1]) + min(P, max((int)0, A[i] - A[i - 1]));
			}
			//cout << dp0[i] << " " << dp1[i] << " " << dp2[i] << " " << dp3[i] << " " << endl;
		}
		cout << min(dp0[N - 1], min(dp1[N - 1], dp2[N - 1])) << endl;
	}
}