#include <deque>
#include <fstream>
#include <iostream>


using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <long long> d;
long long n,k,s,minim=10000001;
int main()
{

    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
      fin>>n;
      d.push_back(n);
    }
    int lenght=n-1;

    while(lenght>=k)
    {
        for(int i=0;i<k;i++)
        {
            if(d[i]<minim)
            {
                minim=d[i];

            }
        }
        s+=minim;
        lenght--;
        d.pop_front();

    }
    fout<<s;


    return 0;
}