#include <cstdio>

using namespace std;
int n,k,i,a[500000],Min[500000],j=0,s,Min1;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d %d",&n,&k);
    for(i=1;i<=n;i++)
    {
        scanf("%d ",&a[i]);
    }
     while(k+j<=n)
    {
        j++;
        Min[j]=100000001;
        Min1=100000001;
    for(i=j;i<=k+j-1;i++)
    {
        scanf("%d ",&a[i]);
        if(a[i]<Min1) Min1=a[i];
    }
    Min[j]=Min1;
    }
    for(i=1;i<=j;i++)
        s=Min[i]+s;
    printf("%d",s);



    return 0;
}