Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python3
import sys
INF = float("inf")
import numpy as np


def solve(N: int, K: int, A: "List[int]", F: "List[int]"):
    A.sort()
    F.sort(reverse=True)
    A = np.asarray(A, dtype=np.int)
    F = np.asarray(F, dtype=np.int)

    Asum = A.sum()

    def isOK(y):
        return Asum-np.minimum(A, y//F).sum() <= K

    def binary_search(x):
        ng = -1
        ok = len(x)
        while abs(ok - ng) > 1:
            mid = (ok + ng)//2
            # print("mid: {}, in ({}, {})".format(mid, ng, ok))
            if isOK(mid):
                ok = mid
            else:
                ng = mid
        return ng, ok

    ng, ok = binary_search(range(A.max()*F.max()))
    print(ok)

    # while k > 0:
    #     p1, a1, f1 = heapq.heappop(h)
    #     p2, a2, f2 = heapq.heappop(h)
    #     p1, p2 = -p1, -p2
    #     sub = min(a1 - math.ceil((p2/f1)-1), k)
    #     a1 -= sub
    #     k -= sub
    #     heapq.heappush(h, (-a1*f1, a1, f1))
    #     heapq.heappush(h, (-a2*f2, a2, f2))
    # # print(h)
    # p, a, f = heapq.heappop(h)
    # print(-p)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    A = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    F = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    solve(N, K, A, F)


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
INF = float("inf")
from bisect import bisect_left


def solve(N: int, K: int, A: "List[int]", F: "List[int]"):
    A.sort()
    F.sort(reverse=True)
    h = []
    for a, f in zip(A, F):
        h.append((a*f, a, f))
    h.sort()
    maxtime = h[-1][0]

    def isOK(y):
        i = bisect_left(h, (y+1, -1, -1))
        counter = 0
        # print(h[i:])
        for p, a, f in h[i:]:
            counter += a-y//f
        return counter <= K

    def binary_search(x):
        ng = -1
        ok = len(x)
        while abs(ok - ng) > 1:
            mid = (ok + ng)//2
            # print("mid: {}, in ({}, {})".format(mid, ng, ok))
            if isOK(mid):
                ok = mid
            else:
                ng = mid
        return ng, ok

    ng, ok = binary_search(range(maxtime))
    print(ok)

    # while k > 0:
    #     p1, a1, f1 = heapq.heappop(h)
    #     p2, a2, f2 = heapq.heappop(h)
    #     p1, p2 = -p1, -p2
    #     sub = min(a1 - math.ceil((p2/f1)-1), k)
    #     a1 -= sub
    #     k -= sub
    #     heapq.heappush(h, (-a1*f1, a1, f1))
    #     heapq.heappush(h, (-a2*f2, a2, f2))
    # # print(h)
    # p, a, f = heapq.heappop(h)
    # print(-p)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    A = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    F = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    solve(N, K, A, F)


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
INF = float("inf")
import math
import heapq
import copy


def solve(N: int, K: int, A: "List[int]", F: "List[int]"):
    h = []
    A.sort()
    F.sort(reverse=True)
    for a, f in zip(A, F):
        heapq.heappush(h, (-a*f, a, f))

    maxtime = heapq.nsmallest(1, h)
    maxtime = -maxtime[0][0]

    def isOK(y):
        hh = copy.copy(h)
        counter = 0
        while len(hh) > 0:
            p, a, f = heapq.heappop(hh)
            if -p > y:
                counter += a-y//f
                if counter > K:
                    return False
            else:
                break
        return counter <= K

    def binary_search(x):
        ng = -1
        ok = len(x)
        while abs(ok - ng) > 1:
            mid = (ok + ng)//2
            # print("mid: {}, in ({}, {})".format(mid, ng, ok))
            if isOK(mid):
                ok = mid
            else:
                ng = mid
        return ng, ok

    ng, ok = binary_search(range(maxtime))
    print(ok)

    # while k > 0:
    #     p1, a1, f1 = heapq.heappop(h)
    #     p2, a2, f2 = heapq.heappop(h)
    #     p1, p2 = -p1, -p2
    #     sub = min(a1 - math.ceil((p2/f1)-1), k)
    #     a1 -= sub
    #     k -= sub
    #     heapq.heappush(h, (-a1*f1, a1, f1))
    #     heapq.heappush(h, (-a2*f2, a2, f2))
    # # print(h)
    # p, a, f = heapq.heappop(h)
    # print(-p)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    A = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    F = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    solve(N, K, A, F)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
INF = float("inf")
from bisect import bisect_left


def solve(N: int, K: int, A: "List[int]", F: "List[int]"):
    A.sort()
    F.sort(reverse=True)
    h = []
    for a, f in zip(A, F):
        h.append((a*f, a, f))
    h.sort()
    maxtime = h[-1][0]

    def isOK(y):
        i = bisect_left(h, (y+1, -1, -1))
        counter = 0
        # print(h[i:])
        for p, a, f in h[i:]:
            counter += a-y//f
        return counter <= K

    def binary_search(x):
        ng = -1
        ok = len(x)
        while abs(ok - ng) > 1:
            mid = (ok + ng)//2
            # print("mid: {}, in ({}, {})".format(mid, ng, ok))
            if isOK(mid):
                ok = mid
            else:
                ng = mid
        return ng, ok

    ng, ok = binary_search(range(maxtime))
    print(ok)

    # while k > 0:
    #     p1, a1, f1 = heapq.heappop(h)
    #     p2, a2, f2 = heapq.heappop(h)
    #     p1, p2 = -p1, -p2
    #     sub = min(a1 - math.ceil((p2/f1)-1), k)
    #     a1 -= sub
    #     k -= sub
    #     heapq.heappush(h, (-a1*f1, a1, f1))
    #     heapq.heappush(h, (-a2*f2, a2, f2))
    # # print(h)
    # p, a, f = heapq.heappop(h)
    # print(-p)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    A = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    F = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    solve(N, K, A, F)


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python3
import sys
INF = float("inf")
import math
import heapq


def solve(N: int, K: int, A: "List[int]", F: "List[int]"):
    h = []
    A.sort()
    F.sort(reverse=True)
    for a, f in zip(A, F):
        heapq.heappush(h, (-a*f, a, f))

    maxtime = heapq.nsmallest(1, h)
    maxtime = -maxtime[0][0]

    def isOK(y):
        hh = h.copy()
        counter = 0
        while len(hh) > 0:
            p, a, f = heapq.heappop(hh)
            if -p > y:
                counter += a-y//f
                if counter > K:
                    return False
            else:
                break
        return counter <= K

    def binary_search(x):
        ng = -1
        ok = len(x)
        while abs(ok - ng) > 1:
            mid = (ok + ng)//2
            # print("mid: {}, in ({}, {})".format(mid, ng, ok))
            if isOK(mid):
                ok = mid
            else:
                ng = mid
        return ng, ok

    ng, ok = binary_search(range(maxtime))
    print(ok)

    # while k > 0:
    #     p1, a1, f1 = heapq.heappop(h)
    #     p2, a2, f2 = heapq.heappop(h)
    #     p1, p2 = -p1, -p2
    #     sub = min(a1 - math.ceil((p2/f1)-1), k)
    #     a1 -= sub
    #     k -= sub
    #     heapq.heappush(h, (-a1*f1, a1, f1))
    #     heapq.heappush(h, (-a2*f2, a2, f2))
    # # print(h)
    # p, a, f = heapq.heappop(h)
    # print(-p)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    A = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    F = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    solve(N, K, A, F)


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
INF = float("inf")
from bisect import bisect_left


def solve(N: int, K: int, A: "List[int]", F: "List[int]"):
    A.sort()
    F.sort(reverse=True)
    h = []
    for a, f in zip(A, F):
        h.append((a*f, a, f))
    h.sort()
    maxtime = h[-1][0]

    def isOK(y):
        i = bisect_left(h, (y+1, -1, -1))
        counter = 0
        # print(h[i:])
        for p, a, f in h[i:]:
            counter += a-y//f
        return counter <= K

    def binary_search(x):
        ng = -1
        ok = len(x)
        while abs(ok - ng) > 1:
            mid = (ok + ng)//2
            # print("mid: {}, in ({}, {})".format(mid, ng, ok))
            if isOK(mid):
                ok = mid
            else:
                ng = mid
        return ng, ok

    ng, ok = binary_search(range(maxtime))
    print(ok)

    # while k > 0:
    #     p1, a1, f1 = heapq.heappop(h)
    #     p2, a2, f2 = heapq.heappop(h)
    #     p1, p2 = -p1, -p2
    #     sub = min(a1 - math.ceil((p2/f1)-1), k)
    #     a1 -= sub
    #     k -= sub
    #     heapq.heappush(h, (-a1*f1, a1, f1))
    #     heapq.heappush(h, (-a2*f2, a2, f2))
    # # print(h)
    # p, a, f = heapq.heappop(h)
    # print(-p)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    A = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    F = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    solve(N, K, A, F)


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
INF = float("inf")
import math
import heapq


def solve(N: int, K: int, A: "List[int]", F: "List[int]"):
    h = []
    A.sort()
    F.sort(reverse=True)
    for a, f in zip(A, F):
        heapq.heappush(h, (-a*f, a, f))
    k = K
    while k > 0:
        p1, a1, f1 = heapq.heappop(h)
        p2, a2, f2 = heapq.heappop(h)
        p1, p2 = -p1, -p2
        sub = min(a1 - math.ceil((p2/f1)-1), k)
        a1 -= sub
        k -= sub
        heapq.heappush(h, (-a1*f1, a1, f1))
        heapq.heappush(h, (-a2*f2, a2, f2))
    # print(h)
    p, a, f = heapq.heappop(h)
    print(-p)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    A = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    F = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    solve(N, K, A, F)


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
INF = float("inf")
from bisect import bisect_left


def solve(N: int, K: int, A: "List[int]", F: "List[int]"):
    A.sort()
    F.sort(reverse=True)
    h = []
    for a, f in zip(A, F):
        h.append((a*f, a, f))
    h.sort()
    maxtime = h[-1][0]

    def isOK(y):
        i = bisect_left(h, (y+1, -1, -1))
        counter = 0
        # print(h[i:])
        for p, a, f in h[i:]:
            counter += a-y//f
        return counter <= K

    def binary_search(x):
        ng = -1
        ok = len(x)
        while abs(ok - ng) > 1:
            mid = (ok + ng)//2
            # print("mid: {}, in ({}, {})".format(mid, ng, ok))
            if isOK(mid):
                ok = mid
            else:
                ng = mid
        return ng, ok

    ng, ok = binary_search(range(maxtime))
    print(ok)

    # while k > 0:
    #     p1, a1, f1 = heapq.heappop(h)
    #     p2, a2, f2 = heapq.heappop(h)
    #     p1, p2 = -p1, -p2
    #     sub = min(a1 - math.ceil((p2/f1)-1), k)
    #     a1 -= sub
    #     k -= sub
    #     heapq.heappush(h, (-a1*f1, a1, f1))
    #     heapq.heappush(h, (-a2*f2, a2, f2))
    # # print(h)
    # p, a, f = heapq.heappop(h)
    # print(-p)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    A = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    F = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    solve(N, K, A, F)


if __name__ == '__main__':
    main()