#include<fstream>
#define maxn 5000020
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int a[maxn],ind[maxn];
long long s;
int main()
{
int n,i,j,x,prim,last,k;
f>>n>>k;
  for(i=1;i<=n;i++)
    f>>a[i];
 prim=1;
 last=0;
 for(i=1;i<=n;i++)
 {
     while(prim<=last&& a[i]<=a[ind[last]])
     last--;
     last+=1;
     ind[last]=i;
     while(ind[prim]<=i-k)
     prim++;
     if(i>=k)
      s+=a[ind[prim]];

 }
 g<<s;
 return 0;
}