#include<fstream>
#include<deque>
#define MAXN 5000005
#define LL long long
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque<LL> q;
LL N,K,A[MAXN],S;
int main() {
      LL i;
	  cin>>N>>K;
	  for(i=1;i<=N;i++)
	              cin>>A[i];
      for(i=1;i<=N;i++) {
	  			while(q.size()>0 && A[i]<=A[q.back()]) q.pop_back();
	            q.push_back(i);
	  if(q.front()==i-K) q.pop_front();
	  if(i>=K) S+=A[q.front()];
	  }
cout<<S;
return 0;
}