#include <iostream>
#include <fstream>

using namespace std;

int v[5000001], Deque[5000001];
int N, K;
int fr = 1, b = 0;
long long S = 0;
int i;

int main()
{
	
	ifstream f("deque.in");
	ofstream o("deque.out");
	f >> N >> K;
	for (i = 1; i <= N; i++)
		f >> v[i];
	for (i = 1; i <= N; i++)
	{
		while (fr <= b && v[i] <= v[Deque[b]])
			b--;
		b++;
		Deque[b] = i;
		if (Deque[fr] == i - K)
			fr++;
		if (i >= K)
			S += v[Deque[fr]];
	}
	o << S;

	
}