Buggy python submission (verdict: Runtime Error):
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

N, K = map(int, input().split())
P = list(map(int, input().split()))
C = list(map(int, input().split()))
if K == 1:
    print(max(C))
    import sys
    sys.exit()
uf = UnionFind(N)
for i in range(N):
    uf.union(i, P[i]-1)

ans = -float("inf")
for x in uf.all_group_members().values():
    n = len(x)
    m_score = [-float("inf")] * n
    sum_c = 0
    for i in x:
        tmp_score = 0
        tmp_pos = i
        sum_c += C[i]
        for j in range(n):
            tmp_pos = P[tmp_pos]
            tmp_pos -= 1
            tmp_score += C[tmp_pos]
            m_score[j] = max(tmp_score, m_score[j])
    if K <= n:
        ans = max(ans, max(m_score[:K]))
    elif sum_c <= 0:
        ans = max(max(m_score), ans)
    else:
        ans = max(sum_c * (K//n) + max(m_score[:(K%n)]), ans)
print(ans)

Fixed submission:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

N, K = map(int, input().split())
P = list(map(int, input().split()))
C = list(map(int, input().split()))
if K == 1:
    print(max(C))
    import sys
    sys.exit()
uf = UnionFind(N)
for i in range(N):
    uf.union(i, P[i]-1)

ans = -float("inf")
for x in uf.all_group_members().values():
    n = len(x)
    m_score = [-float("inf")] * (n+1)
    m_score[0] = 0
    sum_c = 0
    for i in x:
        tmp_score = 0
        tmp_pos = i
        sum_c += C[i]
        for j in range(n):
            tmp_pos = P[tmp_pos]
            tmp_pos -= 1
            tmp_score += C[tmp_pos]
            m_score[j+1] = max(tmp_score, m_score[j+1])
    if sum_c <= 0:
        ans = max(max(m_score[1:]), ans)
    elif K <= n:
        ans = max(ans, max(m_score[1:K+1]))
    elif K % n == 0:
        ans = max(sum_c * (K//n-1) + max(m_score[1:]), ans) 
    else:
        ans = max(sum_c * (K//n) + max(m_score[:(K%n)+1]), ans)
print(ans)

Buggy python submission (verdict: Runtime Error):
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

N, K = map(int, input().split())
P = list(map(int, input().split()))
C = list(map(int, input().split()))
if K == 1:
    print(max(C))
    import sys
    sys.exit()
uf = UnionFind(N)
for i in range(N):
    uf.union(i, P[i]-1)

ans = -float("inf")
for x in uf.all_group_members().values():
    n = len(x)
    m_score = [-float("inf")] * (n+1)
    sum_c = 0
    for i in x:
        tmp_score = 0
        tmp_pos = i
        sum_c += C[i]
        for j in range(n):
            tmp_pos = P[tmp_pos]
            tmp_pos -= 1
            tmp_score += C[tmp_pos]
            m_score[j+1] = max(tmp_score, m_score[j+1])
    if K <= n:
        ans = max(ans, max(m_score[1:K+1]))
    elif sum_c <= 0:
        ans = max(max(m_score), ans)
    else:
        ans = max(sum_c * (K//n) + max(m_score[1:(K%n)+1]), ans)
print(ans)

Fixed submission:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

N, K = map(int, input().split())
P = list(map(int, input().split()))
C = list(map(int, input().split()))
if K == 1:
    print(max(C))
    import sys
    sys.exit()
uf = UnionFind(N)
for i in range(N):
    uf.union(i, P[i]-1)

ans = -float("inf")
for x in uf.all_group_members().values():
    n = len(x)
    m_score = [-float("inf")] * (n+1)
    m_score[0] = 0
    sum_c = 0
    for i in x:
        tmp_score = 0
        tmp_pos = i
        sum_c += C[i]
        for j in range(n):
            tmp_pos = P[tmp_pos]
            tmp_pos -= 1
            tmp_score += C[tmp_pos]
            m_score[j+1] = max(tmp_score, m_score[j+1])
    if sum_c <= 0:
        ans = max(max(m_score[1:]), ans)
    elif K <= n:
        ans = max(ans, max(m_score[1:K+1]))
    elif K % n == 0:
        ans = max(sum_c * (K//n-1) + max(m_score[1:]), ans) 
    else:
        ans = max(sum_c * (K//n) + max(m_score[:(K%n)+1]), ans)
print(ans)

Buggy python submission (verdict: Runtime Error):
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

N, K = map(int, input().split())
P = list(map(int, input().split()))
C = list(map(int, input().split()))
uf = UnionFind(N)
for i in range(N):
    uf.union(i, P[i]-1)

ans = -float("inf")
for x in uf.all_group_members().values():
    n = len(x)
    m_score = [-float("inf")] * (n+1)
    sum_c = 0
    for i in x:
        tmp_score = 0
        tmp_pos = i
        sum_c += C[i]
        for j in range(n):
            tmp_pos = P[tmp_pos]
            tmp_pos -= 1
            tmp_score += C[tmp_pos]
            m_score[j+1] = max(tmp_score, m_score[j+1])
    # if K <= n:
    #     ans = max(ans, max(m_score[:K+1]))
    if sum_c <= 0:
        ans = max(max(m_score), ans)
    else:
        ans = max(sum_c * (K//n) + max(m_score[1:(K%n)+1]), ans)
print(ans)

Fixed submission:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

N, K = map(int, input().split())
P = list(map(int, input().split()))
C = list(map(int, input().split()))
if K == 1:
    print(max(C))
    import sys
    sys.exit()
uf = UnionFind(N)
for i in range(N):
    uf.union(i, P[i]-1)

ans = -float("inf")
for x in uf.all_group_members().values():
    n = len(x)
    m_score = [-float("inf")] * (n+1)
    m_score[0] = 0
    sum_c = 0
    for i in x:
        tmp_score = 0
        tmp_pos = i
        sum_c += C[i]
        for j in range(n):
            tmp_pos = P[tmp_pos]
            tmp_pos -= 1
            tmp_score += C[tmp_pos]
            m_score[j+1] = max(tmp_score, m_score[j+1])
    if sum_c <= 0:
        ans = max(max(m_score[1:]), ans)
    elif K <= n:
        ans = max(ans, max(m_score[1:K+1]))
    elif K % n == 0:
        ans = max(sum_c * (K//n-1) + max(m_score[1:]), ans) 
    else:
        ans = max(sum_c * (K//n) + max(m_score[:(K%n)+1]), ans)
print(ans)