#include <iostream>
#include <fstream>
#include <climits>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int main()
{
    int n,k,x,i,j,s=0,min;
    fin>>n>>k;
    for(i=0;i<n;i=i+k)
    {
        min=INT_MAX;
        for(j=0;j<k;j++)
        {
            fin>>x;
            if(x<min)
                min=x;
        }
        s+=min;
    }
    fout<<s;
    return 0;
}