#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
	int t,k,n,i,j,g,h,count=0,temp,flag;
	unsigned long long int a[500];
	scanf("%d",&t);
	for(i=0;i<t;i++)
	{
		scanf("%d %d",&n,&k);
		count = 0;
		for(j=0;j<n;j++)
		{
			scanf("%llu",&a[j]);
			if(j<(n-1))
				scanf(" ");
		}
		for(j=0;j<(n/k);j++)
		{
			for(h=0;h<(n/k);h++)
			{
				for(g=j;g<(n-k);g=(g+k))
				{
					if(a[g]>a[g+k])
					{
						temp = a[g];
						a[g] = a[g+k];
						a[g+k] = temp;
						count++;
					}
				}
			}
		}
		flag = 0;
		for(j=0;j<(n-1);j++)
		{
			if(a[j]<a[j+1])
				continue;
			else
			{
				flag = 1;
				break;
			}
		}
		if(flag == 0)
		{
			printf("%d\n",count);
		}
		else
			printf("-1\n");
	}
	return 1;
}