#include <fstream>
using namespace std;
#define maxn 5000010
ifstream f("deque.in");
ofstream g("deque.out");
int N, K;
int A[maxn], Deque[maxn];
int Front, Back;
long long Sum;
int main()
{
	int i;
	f>>N>>K;
	for (i = 1; i <= N; i++)
		f>>A[i];
	Front = 1, Back = 0;
	for (i = 1; i <= N; i++)
	{
		while (Front <= Back && A[i] <= A[ Deque[Back] ]) Back--;
		Deque[++Back] = i;
		if (Deque[Front] == i-K) Front++;
		if (i >= K) Sum += A[ Deque[Front]];
	}
	g<<Sum;
	return 0;
}