#include <fstream>

class Deque
{
	
	struct Node
	{
		int data;
		Node *next;
	};
	
	Node *first, *last;
	
public:
	
	Deque() : first(NULL), last(NULL) { }
	
	~Deque()
	{
		while(!empty())
			pop_front();
	}
	
	void push_front(int x)
	{
		if(first == NULL)
		{
			first = new Node();
			first->data = x;
			last = first;
		}
		else
		{
			Node *c = first;
			first = new Node();
			first->data = x;
			first->next = c;
		}
	}
	
	void push_back(int x)
	{
		if(last == NULL)
			push_front(x);
		else
		{
			last->next = new Node();
			last = last->next;
			last->data = x;
		}
	}
	
	void pop_front()
	{
		if(last == first)
		{
			Node *c = first;
			first = last = NULL;
			delete c;
		}
		else
		{
			Node *c = first;
			first = first->next;
			delete c;
		}
	}
	
	void pop_back()
	{
		if(last == first)
			pop_front();
		else
		{
			Node *c = first;
			while(c->next != last)
				c = c->next;
			c->next = NULL;
			delete last;
			last = c;
		}
	}
	
	int front()
	{
		if(empty()) return 0;
		return first->data;
	}
	
	int back()
	{
		if(empty()) return 0;
		return last->data;
	}
	
	bool empty()
	{
		return first == NULL;
	}
	
};

int main()
{
	std::ifstream in("deque.in");
	std::ofstream out("deque.out");
	Deque myDeq;
	int nV;
	int k;
	in >> nV >> k;
	int *nArr = new int[nV + 1];
	for(int i = 1; i <= nV; i++)
		in >> nArr[i];
	long long sum = 0;
	for(int i = 1; i <= nV; i++)
	{
		while(myDeq.front() <= i - k && !myDeq.empty())
			myDeq.pop_front();
		
		while(nArr[myDeq.back()] >= nArr[i] && !myDeq.empty())
			myDeq.pop_back();
			
		myDeq.push_back(i);
		
		if(i >= k) 
			sum += nArr[myDeq.front()];
	}
	out << sum;
	return 0;
}