#include <iostream>
#include <fstream>
#include <deque>
 
int deque[5000000];
int st = 0, dr = -1;

int v[5000000];

int main()
{
	std::ifstream f("deque.in");
	std::ofstream g("deque.out");
 
	int n,k;
	long long rez = 0;
	f >> n >> k;
	for (int i = 0; i < n; ++i)
		f >> v[i];

	for (int i = 0; i < n; ++i)
	{
		while (st <= dr && v[deque[dr]] >= v[i])
			dr--;
		
		deque[++dr] = i;
		 

		if (i < k - 1)continue;

		if (deque[st] <= i - k)
			st++;

		rez += v[deque[st]];
	}

	g << rez;
}