package yukicoder;

import java.util.*;

public class P595 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		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[] dpr = new long[N];
		long[] dpl = new long[N];
		dpl[0] = 1000000000;
		for(int i=1; i<N; i++) {
			dpr[i] = Math.min(Math.min(dpr[i-1], dpl[i-1])+P, dpr[i-1]+Math.max(0, H[i]-H[i-1]));
			dpl[i] = Math.min(Math.min(dpr[i-1], dpl[i-1])+P, dpl[i-1]+Math.max(0, H[i-1]-H[i]));
		}
		System.out.println(Math.min(dpr[N-1], dpl[N-1]));
	}

}