n, k = map(eval, input().split())
ls = [0]
for i in input().split():
    ls.append(ls[-1] + int(i))
# print(ls)
i = 0
p = 0
while i + k < n:
    p = max(p, ls[i + k] - ls[i])
    i += 1
print(ls[-1] - p)