#include<iostream>
using namespace std;


int main()
{
	int t,n,k,i,sum,temp;
	int s;


	
	cin>>t;
	while(t--)
	{
		cin>>n>>k;
		
		sum=0;
		for(i=0;i<n;i++)
		{
			cin>>s;
			if(i<n-n%k)
			{
				if(i%k==0)
					temp=s;
				else
					sum+=s-temp;		
			}
			else
				sum+=s-temp;
		}
		cout<<sum<<endl;
		
	}

	return 0;
}