def f(i, k, N, K, C):
    if i >= N:
        if k > 0:
            return 1000000000000000
        return 0
    if k == K:
        return C[i] + f(i + K + 1, 0, N, K, C)
    return min(C[i] + f(i + K + 1, 0, N, K, C), f(i + 1, k + 1, N, K, C))
N, K = list(map(int, input().split()))
C = list(map(int, input().split()))


print(f(0, 0, N, K, C))