#include<fstream>
#define Nmax 5000010
using namespace std;

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

int N, A[Nmax], deque[Nmax], front, back;
long long i, K, sum;

int main()
{
	fin >> N>>K;
	for (i = 1; i <= N; ++i)
		fin >> 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]];
	}
	fout << sum << '\n';
	return 0;
}