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.

5 3
10 30 40 50 20

30

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

3 1
10 20 10

20

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

2 100
10 10

0

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

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

40

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