#include <stdio.h>
#include <algorithm>
#include <vector>
using namespace std;
int N,K,i,z,temp_,sum;
std::vector<int> A(5000001);
std::vector<int> maxime(5000001);
void move_left()
{
    for(int x=2;x<=K;x++)
        A[x-1]=A[x];
}
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&N,&K);
    A.resize(K+1);
    maxime.resize(K+1);
    for(i=1;i<=N;i++)
    {
        scanf("%d",&temp_);
        if(i<=K)
            A[i]=temp_;
        else
        {
            for(z=1;z<=K;z++)
                maxime[i-K]=max(maxime[i-K],A[z]);
            move_left();
            A[K]=temp_;
        }
    }
    for(i=1;i<=K;i++)
        sum+=A[i];
    printf("%d",sum);
    return 0;
}