#include <stdio.h>
long long s;
int i, j, n, k, m, a[5000001];  
int main()
{
	freopen ("deque.in","r",stdin);
	freopen ("deque.out","w",stdout);
	scanf ("%d%d", &n, &k);
	s = 0;
	for (i = 1;i <= n;i++) scanf ("%d", &a[i]);
	for (i = 1;i <= n - k + 1;i++)
	{
		m = a[i];
		for (j = i + 1;j <= i + k - 1;j++) if (a[j] < m) m = a[j];
		s = s + m;
	}
	printf ("%lld\n", &s);
	return 0;
}