#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000005],d[5000005];
long long n,k,i,front,back,S;
int main()
{
	fin>>n>>k;
	for(i=1;i<=n;i++)
		fin>>v[i];
	front=1;back=1;
	for(i=1;i<=n;i++)
	{
		while(front<=back&&v[i]<=v[d[back]]&&back<=n&&front<=n)
			back--;
		back++;
		d[back]=i;
		if(d[front]==i-k)
			front++;
		if(i>=k)
			S=S+v[d[front]];
	}
	fout<<S;
	return 0;
}