#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,u,p,i,deq[5000005],v[5000005];
long long s;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>v[i];
    for(i=1;i<=n;i++)
    {
      while(p<=u&&v[i]<=v[deq[u]])
        u--;
    deq[++u]=i;
    if(deq[p]==i-k)
        p++;
    if(i>=k)
        s=s+v[deq[p]];
    }

    g<<s;
    return 0;
}