#include<fstream>
#include<deque>
using namespace std;

void main ()
{
	deque <int> q;
	int n, k, *v;;
	long long sum = 0;
	ifstream f ("deque.in");
	f >> n >> k;
	v = new int[n];
	for (int i = 0; i < n; i++)
	{
		f >> v[i];
		while (!q.empty() && v[q.back()] > v[i])
			q.pop_back();
		q.push_back(i);
		if (i >= k - 1)
		{
			sum += v[q.front()];
			if (q.front() == i + 1 - k)
				q.pop_front();
		}
	}
	f.close();
	ofstream g ("deque.out");
	g << sum;
	g.close();
}