def alien_dp(cost):
    dpa = (0, 0)
    dpb = (-INF, -1)
    for i in range(N):
        ndpa = max((dpa[0] + A[i], dpa[1]), (dpb[0] + A[i] - cost, dpb[1] - 1))
        ndpb = max((dpa[0] + B[i] - cost, dpa[1] - 1), (dpb[0] + B[i], dpb[1]))
        dpa = ndpa
        dpb = ndpb
    score, cnt = max(dpa, dpb)
    cnt =- cnt
    return score, cnt

score, cnt = alien_dp(0)
if cnt <= K:
    print(score)
    exit()
    
ng, ok = 0, 1 << 60
while ok - ng > 1:
    med = (ok + ng) // 2
    score, cnt = alien_dp(med)
    if cnt > K:
        ng = med
    else:
        ok = med
    
score, cnt = alien_dp(ok)
print(score + ok * K)