Score : 100 points

Problem Statement

There are N stones, numbered 1, 2, \ldots, N. For each i (1 \leq i \leq N), the height of Stone i is h_i.

There is a frog who is initially on Stone 1. He will repeat the following action some number of times to reach Stone N:

  • If the frog is currently on Stone i, jump to one of the following: Stone i + 1, i + 2, \ldots, i + K. Here, a cost of |h_i - h_j| is incurred, where j is the stone to land on.

Find the minimum possible total cost incurred before the frog reaches Stone N.

Constraints

  • All values in input are integers.
  • 2 \leq N \leq 10^5
  • 1 \leq K \leq 100
  • 1 \leq h_i \leq 10^4

Input

Input is given from Standard Input in the following format:

N K
h_1 h_2 \ldots h_N

Output

Print the minimum possible total cost incurred.

Sample Input 1

5 3
10 30 40 50 20

Sample Output 1

30

If we follow the path 1 → 2 → 5, the total cost incurred would be |10 - 30| + |30 - 20| = 30.

Sample Input 2

3 1
10 20 10

Sample Output 2

20

If we follow the path 1 → 2 → 3, the total cost incurred would be |10 - 20| + |20 - 10| = 20.

Sample Input 3

2 100
10 10

Sample Output 3

0

If we follow the path 1 → 2, the total cost incurred would be |10 - 10| = 0.

Sample Input 4

10 4
40 10 20 70 80 10 20 70 80 60

Sample Output 4

40

If we follow the path 1 → 4 → 8 → 10, the total cost incurred would be |40 - 70| + |70 - 70| + |70 - 60| = 40.