#include <cstdio>

using namespace std;
int i,a[5000003],n,k,b[5000003],j,u,p;
long long Min;
void pune(int i)
{
  while(u>=p && a[b[u]]>a[i])
  {b[u]=0;--u;}
  ++u;
  b[u]=i;
}

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);

    scanf("%d %d\n",&n,&k);

    for(i=1;i<=n;++i)
    scanf("%d",&a[i]);

    p=1;u=0;

    for(i=1;i<k;++i)
    pune(i);

    for(i=k;i<=n;++i)
    {
      pune(i);
      Min+=a[b[p]];
      if(i-b[p]==k-1) {b[p]=0;p++;}

    }

     printf("%lld\n",Min);





    return 0;
}