Buggy python submission (verdict: Time Limit Exceeded):
from itertools import accumulate
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**9)

def solve():
    N, K = map(int, input().split())
    Ps = list(map(lambda x: int(x)-1, input().split()))
    Cs = list(map(int, input().split()))

    cycless = [[] for _ in range(N)]
    useds = [0] * N
    for no in range(N):
        if useds[no]: continue
        x = no
        while True:
            useds[x] = 1
            cycless[no].append(Cs[x])
            x = Ps[x]
            if x == no:
                break

#    for no in range(N):
#        print('# no:', no, '/ cycless[no]:', cycless[no], file=sys.stderr)

    ans = -float('inf')
    for no in range(N):
        if not cycless[no]: continue
        L = len(cycless[no])
        accCycles = list(accumulate([0]+cycless[no]+cycless[no]+cycless[no]))
        sumC = sum(cycless[no])
#        print('\n# no:', no, '/ sumC:', sumC, file=sys.stderr)
        if sumC > 0:
            num = K//L
            if num > 1:
                num -= 1
                score = -float('inf')
#                print('# K:', K, file=sys.stderr)
                for M in range(0, L + K%L+1):
                    for st in range(L):
                        s = accCycles[st+M] - accCycles[st]
                        if s > score:
                            score = s
                score += sumC * num
            else:
                score = -float('inf')
                for M in range(1, K+1):
                    for st in range(L):
                        s = accCycles[st+M] - accCycles[st]
                        if s > score:
                            score = s
        elif sumC == 0:
            num = K//L
            if num > 1:
                score = -float('inf')
                for M in range(0, 2*L+1):
                    for st in range(L):
                        s = accCycles[st+M] - accCycles[st]
                        if s > score:
                            score = s
            else:
                score = -float('inf')
                for M in range(1, K+1):
                    for st in range(L):
                        s = accCycles[st+M] - accCycles[st]
                        if s > score:
                            score = s
        else:
            score = -float('inf')
            for M in range(1, (K if K <= L else L)+1):
                for st in range(L):
                    s = accCycles[st+M] - accCycles[st]
                    if s > score:
                        score = s
        if score > ans:
            ans = score
#        print('# no:', no, '/ score:', score, file=sys.stderr)

    print(ans)


solve()


Fixed submission:
from itertools import accumulate
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**9)

def solve():
    N, K = map(int, input().split())
    Ps = list(map(lambda x: int(x)-1, input().split()))
    Cs = list(map(int, input().split()))

    cycless = [[] for _ in range(N)]
    useds = [0] * N
    for no in range(N):
        if useds[no]: continue
        x = no
        while True:
            useds[x] = 1
            cycless[no].append(Cs[x])
            x = Ps[x]
            if x == no:
                break

#    for no in range(N):
#        print('# no:', no, '/ cycless[no]:', cycless[no], file=sys.stderr)

    ans = -float('inf')
    for no in range(N):
        if not cycless[no]: continue
        L = len(cycless[no])
        accCycles = list(accumulate([0]+cycless[no]+cycless[no]+cycless[no]))
        sumC = sum(cycless[no])
#        print('\n# no:', no, '/ sumC:', sumC, file=sys.stderr)
        if sumC > 0:
            num = K//L
            if num > 1:
                num -= 1
                score = -float('inf')
#                print('# K:', K, file=sys.stderr)
                for M in range(0, L + K%L+1):
                    for st in range(L):
                        s = accCycles[st+M] - accCycles[st]
                        if s > score:
                            score = s
                score += sumC * num
            else:
                score = -float('inf')
                for M in range(1, K+1):
                    for st in range(L):
                        s = accCycles[st+M] - accCycles[st]
                        if s > score:
                            score = s
        elif sumC == 0:
            num = K//L
            if num > 1:
                score = -float('inf')
                for M in range(0, 2*L+1):
                    for st in range(L):
                        s = accCycles[st+M] - accCycles[st]
                        if s > score:
                            score = s
            else:
                score = -float('inf')
                for M in range(1, K+1):
                    for st in range(L):
                        s = accCycles[st+M] - accCycles[st]
                        if s > score:
                            score = s
        else:
            score = -float('inf')
            for M in range(1, (K if K <= L else L)+1):
                for st in range(L):
                    s = accCycles[st+M] - accCycles[st]
                    if s > score:
                        score = s
        if score > ans:
            ans = score
#        print('# no:', no, '/ score:', score, file=sys.stderr)

    print(ans)


solve()