#include <cstdio>
#include <queue>

using namespace std;
const int NMAX=1000000;
int v[NMAX+5];
typedef pair<int,int>ii;
deque<ii>q;
int main(){
    int n,k,i,s=0;
	scanf("%d%d",&n,&k);
	for(i=1;i<=n;i++)
		scanf("%d",&v[i]);
	for(i=1;i<=n;i++){
		while(!q.empty() && q.back().first>=v[i])
			q.pop_back();
		q.push_back(ii(v[i],i));
		while(!q.empty() && i-q.front().second+1>k)
			q.pop_front();
		if(i>=k)
			s=s+q.front().first;
	}
	printf("%d ",s);
    return 0;
}