#include<fstream.h>

#define xx 5000001

ifstream fin("deque.in");
ofstream fout("deque.out");

int n,k,v[xx],deque[xx],li,ls;
long long suma;

int main()
{
    int i;
    
    fin>>n>>k;
    for(i=1;i<=n;i++)
      fin>>v[i];
    
    for(li=1,ls=0,suma=0,i=1;i<=n;i++)
    {
       while(li<=ls && v[i]<=v[deque[ls]]) ls--;
       
       deque[++ls]=i;
       
       if(deque[li]==i-k) li++;
       
       if(i>=k)
          suma+=v[deque[li]];
    }
    
    fout<<suma<<'\n';
    fout.close();
    return 0;
}