#include <fstream>

#define maxn 5000010

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int n, k;
int v[maxn], Deque[maxn];
int Front, Back;
long long Sum;

int main()
{
	int i;

	fin>>n>>k;
	for (i=1; i<=n; i++)
		fin>>v[i];

	Front=1, Back=0;

	for (i=1; i<=n; i++)
	{
		while(Front<=Back && v[i]<=v[Deque[Back]])
            Back--;
		Deque[++Back] = i;
		if (Deque[Front] == i-k)
            Front++;
		if (i>=k)
            Sum += v[Deque[Front]];
	}

	fout<<Sum;

	return 0;
}