n, k = map(int, input().split())  # n:n个城市 k:半径
a = list(map(int, input().split()))  # a有n-1个整数

# 找到n-1个整数中k个连续的和最大的数
m = 0
t = 0
if k >= n:
    k = n-1
    print(0)
else:
    for i in range(0, k):
        m += a[i]

    for i in range(0, n - k - 1):
        t = m - a[i] + a[k + i]
        if t > m:
            m = t

    ans = sum(a) - m
    print(ans)