#include <bits/stdc++.h>
 
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int n, k, a[5000006];
long long sum = 0;
deque <int> d;

int main()
{
	int i, x;
	fin >> n >> k;

	for (i = 1; i <= n; i++)
	{
		fin >> a[i];
		x = a[i];
		while (!d.empty() and a[d.back()] >= x)
			d.pop_back();
		d.push_back(i);
		if (i >= k)
		{
			if (d.front() == i - k)
				d.pop_front();
			sum += a[d.front()];
		}
	}

	fout << sum << "\n";

	return 0;
}