#include <fstream.h>
long v[5000001],v1[5000001];     //000
long long s;
int main()
{long n,k,i,c=0,j,a,l;
ifstream q("deque.in");
ofstream w("deque.out");
cin>>n>>k;
v[1]=10000001;
for(i=1;i<k+1;i++)
  {cin>>a;
  c++;
  while(a<v[c-1]&&c>1)
   c--;
  v[c]=a;
  v1[c]=i;
  }
  s=v[1];
  l=1;
  for(i=i;i<n+1;i++)
    {if(v1[l]==i-k)
      l++;
    cin>>a;
    c++;
    while(a<v[c-1]&&c>l)
     c--;
    v[c]=a;
    v1[c]=i;
    s=s+v[l];}
cout<<s;
return 0;}