#include <iostream>
#include <fstream>

using namespace std;
int v[100000];
int main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    int n,nr,cnt=0,min=2100000000,sum;
    cin>>n>>nr;
    for(int i=0;i<n;i++)
    {
        cin>>v[i];
    }

    for(int i=0;i<n/nr;i+=nr)
    {
        for(int j=i+1;j<i+nr;j++)
        {
            if(v[j]<min)
                min=v[j];
        }
        sum+=min;
        min=2100000000;
    }

    cout<<sum;

    return 0;
}