Minimum Asphalt to repair all damaged locations of the road

Can anyone help me to understand the logic?

There is a highway that has damages at N (4<=N<=100) locations. Each damage location is represented by a number a (0<=a<=10000). You need to repair these damages with Asphalt. The damage is repaired with these rules:

  1. Asphalt can be spread on the road with a minimum stretch of K (1<=K<=10000) i.e. each time you put asphalt, it will be spread to k consecutive locations. eg. if the damage is at locations 2, 5 and K=3 then the first asphalt spread is from 0-2 or 1-3 or 2-4 and the second is from 3-5 or 4-6 or 5-7.
  2. You need to spread minimum Asphalt to repair all damaged locations of the road. For the above example, the minimum asphalt required is 4 units ( 2-4 and 3-5) because 3-4 is overlapping.

Example test cases:

Input:-

N K

A[0] A[1] ……… A[N-1]

Output:-

Minimum Asphalt area to repair all damages.

#first case

10 2

0 10 2 12 4 14 6 16 8 18

output: 15

#second case

4 3

3 9 11 8

output: 7

#third case

8 3

2 7 20 5 19 9 6 22

output: 12