#include <fstream>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int i,fr,ba,s,n,k;
int v[5*1001*1001],dq[5*1001*1001];
int main()
{
f>>n>>k;
for(i=1;i<=n;i++) f>>v[i];;
   fr=1;
   ba=0;
   for(i=1;i<=n;i++){
    while(fr<=ba&&v[i]<=v[dq[ba]]) ba--;
    dq[++ba]=i;
    if(dq[fr]==i-k) fr++;
if(i>=k) s+=v[dq[fr]];



   }
   g<<s;
    return 0;
}