#include <bits/stdc++.h>
using namespace std;

int main(){

	int n,k;
	cin>>n>>k;
	int nn[n];
	double bsum=0.0;
	double ssum=0.0;
	double vsum=0.0;
	double temp=0.0;
	for (int i = 0; i < n; ++i) {
		cin>>nn[i];
		}
		sort(nn,nn+n,greater<int>());

if(n%k==k-1){
		for (int i = 0; i < n/k ; ++i) {
			temp+=nn[i];
		}
		ssum=temp/(n/k);
		temp=0;
		for (int i = n-1; i >( n-1)-(n/k)-1 ; --i) {
					temp+=nn[i];
		}
		vsum=temp/((n/k)+1);
		cout<<floor(ssum-vsum+0.5)<<endl;
}else {
    for (int i = 0; i < n/k ; ++i) {
		temp+=nn[i];
	}
	ssum=temp/(n/k);
	temp=0.0;
	for (int i = n-1; i >( n-1)-(n/k) ; --i) {
				temp+=nn[i];
	}
	vsum=(double)temp/((n/k));
	cout<<ceil(ssum-vsum+0.5)<<endl;
	return 0;
}


}