#include <fstream>
#include <math.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,p,u,v[5000010],d[5000010];
long long sol;
int main() {
	fin>>n>>k;
	for (i=1;i<=n;i++)
		fin>>v[i];
	p=1; u=1; d[1]=1;
	for (i=2;i<=n;i++) {
		while (v[i]<v[d[u]]&&p<=u)
			u--;
		u++; d[u]=i;
		if (i-d[p]==k)
			p++;
		if (i>=k)
			sol+=v[d[p]];
	}
	fout<<sol;
	return 0;
}