#include <fstream>

using namespace std;

ifstream fi("deque.in");
ofstream fo("deque.out");

int v[5000001], d[5000001];

int main()
{
	int n, k, i, p, q, sum = 0;
	fi >> n >> k;
	p = q = 1;
	d[p] = 1;
	sum = 0;
	for (i = 2; i <= n; i++)
	{
		//intra v[i]
		while (p <= q && v[d[q]] >= v[i]) q--;
		q++;
		d[q] = i;
		if (d[p] < i - k + 1)p++;
		sum += v[d[p]];
	}
	fo << sum;
}