Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/python3

import math
import sys


DEBUG = False


def inp():
    return sys.stdin.readline().rstrip()


def dprint(*value, sep=' ', end='\n'):
    if DEBUG:
        print(*value, sep=sep, end=end)


def solve(N, A):
    allxor = 0
    for a in A:
        allxor ^= a

    B = [0] * N

    ans = 0
    bcount = 0
    for bit in range(61, -1, -1):
        mask = 1 << bit
        if allxor & mask:
            ans <<= 1
            ans |= 1
            continue

        bset = set()
        for i in range(N):
            b = B[i]
            b <<= 1
            b |= (A[i] & mask) >> bit
            B[i] = b
            bset.add(b)
        bcount += 1

        full_bit = (1 << bcount) - 1

        blist = list(bset)
        blist1 = blist[:len(blist) // 2]
        blist2 = blist[len(blist) // 2:]

        r1 = set([0])
        for b in blist1:
            for c in list(r1):
                r1.add(b ^ c)

        r2 = set([0])
        for b in blist2:
            for c in list(r2):
                r2.add(b ^ c)

        best = full_bit - 1
        for b1 in r1:
            if b1 ^ full_bit in r2:
                best = full_bit
                break

        bestb = best & 1
        ans <<= 1
        ans |= bestb

        if bestb == 0:
            for i in range(N):
                B[i] >>= 1
            bcount -= 1

    return ans + (ans ^ allxor)


def main():
    N = int(inp())
    A = [int(e) for e in inp().split()]
    print(solve(N, A))


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/python3

import math
import os
import sys


DEBUG = 'DEBUG' in os.environ


def inp():
    return sys.stdin.readline().rstrip()


def dprint(*value, sep=' ', end='\n'):
    if DEBUG:
        print(*value, sep=sep, end=end)


def solve(N, A):
    allxor = 0
    for a in A:
        allxor ^= a

    while len(A) < 61:
        A.append(0)
    M = len(A)

    row = 0
    ans = 0
    for bi in range(61, -1, -1):
        b = 1 << bi
        if b & allxor:
            ans |= b
            continue

        if not (A[row] & b):
            j = -1
            for i in range(row + 1, M):
                if A[i] & b:
                    j = i
                    break
            if j == -1:
                continue

            A[row], A[j] = A[j], A[row]

        assert A[row] & b
        if not (ans & b):
            ans ^= A[row]

        for i in range(row + 1, M):
            if A[i] & b:
                A[i] ^= A[row]
            assert not (A[i] & b)

        row += 1

    return ans + (ans ^ allxor)


def main():
    N = int(inp())
    A = [int(e) for e in inp().split()]
    print(solve(N, A))


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/python3

import math
import sys


DEBUG = False


def inp():
    return sys.stdin.readline().rstrip()


def dprint(*value, sep=' ', end='\n'):
    if DEBUG:
        print(*value, sep=sep, end=end)


def solve(N, A):
    allxor = 0
    for a in A:
        allxor ^= a

    B = [0] * N

    ans = 0
    bcount = 0
    for bit in range(61, -1, -1):
        mask = 1 << bit
        if allxor & mask:
            ans <<= 1
            ans |= 1
            continue

        bset = set()
        for i in range(N):
            b = B[i]
            b <<= 1
            b |= (A[i] & mask) >> bit
            B[i] = b
            bset.add(b)
        bcount += 1

        full_bit = (1 << bcount) - 1
        rset = set([0])
        for b in bset:
            for c in set(rset):
                rset.add(b ^ c)
            if full_bit in rset:
                break

        best = full_bit if full_bit in rset else full_bit - 1
        assert best in rset
        bestb = best & 1
        ans <<= 1
        ans |= bestb

        if bestb == 0:
            for i in range(N):
                B[i] >>= 1
            bcount -= 1

    return ans + (ans ^ allxor)


def main():
    N = int(inp())
    A = [int(e) for e in inp().split()]
    print(solve(N, A))


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/python3

import math
import os
import sys


DEBUG = 'DEBUG' in os.environ


def inp():
    return sys.stdin.readline().rstrip()


def dprint(*value, sep=' ', end='\n'):
    if DEBUG:
        print(*value, sep=sep, end=end)


def solve(N, A):
    allxor = 0
    for a in A:
        allxor ^= a

    while len(A) < 61:
        A.append(0)
    M = len(A)

    row = 0
    ans = 0
    for bi in range(61, -1, -1):
        b = 1 << bi
        if b & allxor:
            ans |= b
            continue

        if not (A[row] & b):
            j = -1
            for i in range(row + 1, M):
                if A[i] & b:
                    j = i
                    break
            if j == -1:
                continue

            A[row], A[j] = A[j], A[row]

        assert A[row] & b
        if not (ans & b):
            ans ^= A[row]

        for i in range(row + 1, M):
            if A[i] & b:
                A[i] ^= A[row]
            assert not (A[i] & b)

        row += 1

    return ans + (ans ^ allxor)


def main():
    N = int(inp())
    A = [int(e) for e in inp().split()]
    print(solve(N, A))


if __name__ == '__main__':
    main()