#include<fstream>
using namespace std;
const int MAXN=5000010;
long long v[MAXN],deque[MAXN];
long long suma=0;
int n,k,i,inc=1,sf=0;
ifstream fin("deque.in");
ofstream fout("deque.out");
int main()
{
	fin>>n>>k;
	for (i=1;i<=n;++i)
		fin>>v[i];

	for (i=1;i<=n;++i)
	{
		while (inc<=sf && v[i]<v[deque[sf]]) --sf;
		deque[++sf]=i;
		if (deque[inc]==i-k)
			++inc;
		if (i>=k)
			suma+=v[deque[inc]];
	}
	fout<<suma<<'\n';
	fin.close();
	fout.close();
	return 0;
}