import java.util.Arrays;

public class Main {

	private static void solve() {
		int n = ni();
		long p = nl();
		long[] h = nal(n);
		
		long[] f = new long[n];
		f[0] = h[0];
		int ptr = 0;
		for (int i = 0; i < n; i ++) {
			if (f[ptr] != h[i]) {
				f[++ ptr] = h[i];
			}
		}
		h = Arrays.copyOf(f, ptr + 1);
		n = ptr + 1;
		f = new long[n];
		ptr = 0;

		if (h[0] < h[1]) {
			f[ptr ++] = h[0];
		}
			
		for (int i = 1; i < n - 1; i ++) {
			if (h[i - 1] > h[i] && h[i] < h[i + 1]) {
				f[ptr ++] = h[i];
			} else if (h[i - 1] < h[i] && h[i] > h[i + 1]) {
				f[ptr ++] = h[i];
			}
		}
		if (f[ptr] != h[n - 1])
			f[ptr ++] = h[n - 1];
		
		long ret = 0;
		for (int i = 0; i < ptr - 1; i ++) {
			
			if (f[i] < f[i + 1]) {
				if (i == ptr - 2) {
					ret += Math.min(p, f[i + 1] - f[i]);
				} else {
					ret += Math.min(p * 2, f[i + 1] - f[i]);
				}
				i ++;
			}
		}
		System.out.println(ret);
	}

	public static void main(String[] args) {
		new Thread(null, new Runnable() {
			@Override
			public void run() {
				long start = System.currentTimeMillis();
				String debug = args.length > 0 ? args[0] : null;
				if (debug != null) {
					try {
						is = java.nio.file.Files.newInputStream(java.nio.file.Paths.get(debug));
					} catch (Exception e) {
						throw new RuntimeException(e);
					}
				}
				reader = new java.io.BufferedReader(new java.io.InputStreamReader(is), 32768);
				solve();
				out.flush();
				tr((System.currentTimeMillis() - start) + "ms");
			}
		}, "", 64000000).start();
	}

	private static java.io.InputStream is = System.in;
	private static java.io.PrintWriter out = new java.io.PrintWriter(System.out);
	private static java.util.StringTokenizer tokenizer = null;
	private static java.io.BufferedReader reader;

	public static String next() {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new java.util.StringTokenizer(reader.readLine());
			} catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
		return tokenizer.nextToken();
	}

	private static double nd() {
		return Double.parseDouble(next());
	}

	private static long nl() {
		return Long.parseLong(next());
	}

	private static int[] na(int n) {
		int[] a = new int[n];
		for (int i = 0; i < n; i++)
			a[i] = ni();
		return a;
	}

	private static char[] ns() {
		return next().toCharArray();
	}

	private static long[] nal(int n) {
		long[] a = new long[n];
		for (int i = 0; i < n; i++)
			a[i] = nl();
		return a;
	}

	private static int[][] ntable(int n, int m) {
		int[][] table = new int[n][m];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				table[i][j] = ni();
			}
		}
		return table;
	}

	private static int[][] nlist(int n, int m) {
		int[][] table = new int[m][n];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				table[j][i] = ni();
			}
		}
		return table;
	}

	private static int ni() {
		return Integer.parseInt(next());
	}

	private static void tr(Object... o) {
		if (is != System.in)
			System.out.println(java.util.Arrays.deepToString(o));
	}
}