import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		new Main().run();
	}

	static void run() {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long p = sc.nextLong();
		long[] h = new long[n];
		for (int i = 0; i < n; ++i) {
			h[i] = sc.nextLong();
		}
		long[][] dp = new long[n][2];
		for (int i = 0; i < n; ++i) {
			dp[i][0] = Long.MAX_VALUE / 3;
			dp[i][1] = Long.MAX_VALUE / 3;
		}
		dp[0][0] = 0;
		dp[0][1] = p;
		for (int i = 1; i < n; ++i) {
			dp[i][0] = Math.min(dp[i][0], dp[i - 1][0] + Math.max(0, h[i] - h[i - 1]));
			dp[i][0] = Math.min(dp[i][0], dp[i - 1][1] + Math.max(0, h[i] - h[i - 1]));
			dp[i][1] = Math.min(dp[i][1], dp[i - 1][0] + p);
			dp[i][1] = Math.min(dp[i][1], dp[i - 1][1] + p);
			dp[i][1] = Math.min(dp[i][1], dp[i - 1][1] + Math.max(0, h[i - 1] - h[i]));
		}
		System.out.println(Math.min(dp[n - 1][0], dp[n - 1][1]));
	}

	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}