#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int main()
{
	long long int n, k, i, sum = 0, a[5000001];
	deque <int> dq;
	fin >> n >> k;
	for (i = 1; i <= n; i++)
	{
		fin >> a[i];
	}
	for (i = 1; i <= n; i++)
	{
		while (!dq.empty() && dq.front() < i - k + 1) dq.pop_front();
		while (!dq.empty() && a[dq.back()] > a[i])dq.pop_back();
		dq.push_back(i);
		if (i >= k)
		{
			sum += a[dq.front()];
		}


	}
	fout << sum;
}