A9172. K-Periodic Array

This task will exclusively concentrate only on the arrays where all elements equal 1 and/or 2.

Array $a$ is $k$ -period if its length is divisible by $k$ and there is such array $b$ of length $k$ , that $a$ is represented by array $b$ written exactly  times consecutively. In other words, array $a$ is $k$ -periodic, if it has period of length $k$ .

For example, any array is $n$ -periodic, where $n$ is the array length. Array $[2,1,2,1,2,1]$ is at the same time 2-periodic and 6-periodic and array $[1,2,1,1,2,1,1,2,1]$ is at the same time 3-periodic and 9-periodic.

For the given array $a$ , consisting only of numbers one and two, find the minimum number of elements to change to make the array $k$ -periodic. If the array already is $k$ -periodic, then the required value equals $0$ .

The first line of the input contains a pair of integers $n$ , $k$ ( $1<=k<=n<=100)$ , where $n$ is the length of the array and the value $n$ is divisible by $k$ . The second line contains the sequence of elements of the given array $a_{1},a_{2},...,a_{n}$ ( $1<=a_{i}<=2$ ), $a_{i}$ is the $i$ -th element of the array.

Print the minimum number of array elements we need to change to make the array $k$ -periodic. If the array already is $k$ -periodic, then print 0.

In the first sample it is enough to change the fourth element from 2 to 1, then the array changes to $[2,1,2,1,2,1]$ .

In the second sample, the given array already is 4-periodic.

In the third sample it is enough to replace each occurrence of number two by number one. In this case the array will look as $[1,1,1,1,1,1,1,1,1]$ — this array is simultaneously 1-, 3- and 9-periodic.