N, K = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

INF = 1 << 60
ODD = K % 2
EVEN = ODD ^ 1
K2 = K // 2 if EVEN else (K - 1) // 2

def max_score(a: tuple[int,int], b: tuple[int,int]): 
    if a[0] != b[0]:
        return max(a, b)
    else:
        return min(a, b)
    
def alien_dp(cost: int):
    dpa = (0, 0)
    dpb = (-INF, 0)
    for i in range(N):
        ndpa = max_score((dpa[0] + A[i], dpa[1]),(dpb[0] + A[i] - cost * ODD, dpb[1] + ODD))
        ndpb = max_score((dpa[0] + B[i] - cost * EVEN, dpa[1] + EVEN), (dpb[0] + B[i], dpb[1]))
        dpa = ndpa
        dpb = ndpb
    return max(dpa, dpb)
    
score, cnt = alien_dp(0)
if cnt <= K2:
    print(score)
    exit
    
ng, ok = 0, INF
while ok - ng > 1:
    med = (ng + ok) // 2
    score, cnt = alien_dp(med)
    if cnt > K2:
        ng = med
    else:
        ok = med
score, cnt = alien_dp(ok)
print(score + ok * K2)