#include <cstdio>
#define min(a, b) (a < b ? a : b)
int a[3005];
int main()
{
	int n, m, tot = 0, ans = 0x7fffffff;
	scanf("%d %d", &n, &m);
	for (int i = 1; i < m; i++)
	{
		scanf("%d", &a[i]);
		tot += a[i];
	}
	for (int i = m; i <= n; i++)
	{
		scanf("%d", &a[i]);
		tot += a[i], ans = min(ans, tot), tot -= a[tot -= i - m + 1];
	}
	printf("%d", ans);
	return 0;
}