Buggy python submission (verdict: Time Limit Exceeded):
# from math import log2
from math import log
from bisect import bisect_left


def log2(x):
    return log(x, 2)


def getComp(n):
    return (1 << (1 + int(log2(n)))) - n


N = int(input())
A = [int(s) for s in input().split()]
A.sort()

count = 0
i = len(A)
while i > 0:
    i -= 1
    comp = getComp(A[i])
    j = bisect_left(A, comp)
    if i == j or A[j] != comp:
        continue
    if i < j:
        A.pop(j)
        A.pop(i)
    else:
        A.pop(i)
        A.pop(j)
    count += 1
    i -= 1

print(count)


Fixed submission:
# from math import log2
from math import log
from bisect import bisect_left


def log2(x):
    return log(x, 2)


def getComp(n):
    return (1 << (1 + int(log2(n)))) - n


N = int(input())
A = [int(s) for s in input().split()]
A.sort()
B = []
C = []
i = 0
while i < len(A):
    j = i
    count = 1
    while i+1 < len(A) and A[j] == A[i+1]:
        count += 1
        i += 1
    B.append(A[j])
    C.append(count)
    i += 1

count = 0
i = len(B) - 1
while i >= 0:
    comp = getComp(B[i])
    j = bisect_left(B, comp)
    if i == j and C[i] < 2:
        i -= 1
        continue
    if B[j] != comp:
        i -= 1
        continue
    if not C[i] or not C[j]:
        i -= 1
        continue
    C[i] -= 1
    C[j] -= 1
    count += 1

print(count)

Buggy python submission (verdict: Runtime Error):
# from math import log2
from math import log
from bisect import bisect_left


def log2(x):
    return log(x, 2)


def getComp(n):
    return (1 << (1 + int(log2(n)))) - n


N = int(input())
A = [int(s) for s in input().split()]
A.sort()
avail = [True for _ in range(len(A))]

count = 0
for i in range(len(A) - 1, -1, -1):
    if not avail[i]:
        continue
    comp = getComp(A[i])
    j = bisect_left(A, comp)
    while True:
        if A[j] != comp:
            break
        if i == j or not avail[j]:
            j += 1
            continue
        avail[i] = False
        avail[j] = False
        count += 1
        break

print(count)


Fixed submission:
# from math import log2
from math import log
from bisect import bisect_left


def log2(x):
    return log(x, 2)


def getComp(n):
    return (1 << (1 + int(log2(n)))) - n


N = int(input())
A = [int(s) for s in input().split()]
A.sort()
B = []
C = []
i = 0
while i < len(A):
    j = i
    count = 1
    while i+1 < len(A) and A[j] == A[i+1]:
        count += 1
        i += 1
    B.append(A[j])
    C.append(count)
    i += 1

count = 0
i = len(B) - 1
while i >= 0:
    comp = getComp(B[i])
    j = bisect_left(B, comp)
    if i == j and C[i] < 2:
        i -= 1
        continue
    if B[j] != comp:
        i -= 1
        continue
    if not C[i] or not C[j]:
        i -= 1
        continue
    C[i] -= 1
    C[j] -= 1
    count += 1

print(count)

Buggy python submission (verdict: Runtime Error):
from math import log2
from bisect import bisect_left


def getComp(n):
    return (1 << (1 + int(log2(n)))) - n


N = int(input())
A = [int(s) for s in input().split()]
A.sort()
avail = [True for _ in range(len(A))]

count = 0
for i in range(len(A) - 1, -1, -1):
    if not avail[i]:
        continue
    comp = getComp(A[i])
    j = bisect_left(A, comp)
    while True:
        if A[j] != comp:
            break
        if i == j or not avail[j]:
            j += 1
            continue
        avail[i] = False
        avail[j] = False
        count += 1
        break

print(count)


Fixed submission:
# from math import log2
from math import log
from bisect import bisect_left


def log2(x):
    return log(x, 2)


def getComp(n):
    return (1 << (1 + int(log2(n)))) - n


N = int(input())
A = [int(s) for s in input().split()]
A.sort()
B = []
C = []
i = 0
while i < len(A):
    j = i
    count = 1
    while i+1 < len(A) and A[j] == A[i+1]:
        count += 1
        i += 1
    B.append(A[j])
    C.append(count)
    i += 1

count = 0
i = len(B) - 1
while i >= 0:
    comp = getComp(B[i])
    j = bisect_left(B, comp)
    if i == j and C[i] < 2:
        i -= 1
        continue
    if B[j] != comp:
        i -= 1
        continue
    if not C[i] or not C[j]:
        i -= 1
        continue
    C[i] -= 1
    C[j] -= 1
    count += 1

print(count)

Buggy python submission (verdict: Time Limit Exceeded):
from math import log2
from bisect import bisect_left


def getComp(n):
    return (1 << (1 + int(log2(n)))) - n


N = int(input())
A = [int(s) for s in input().split()]
A.sort()
avail = [True for _ in range(len(A))]

count = 0
for i in range(len(A) - 1, -1, -1):
    if not avail[i]:
        continue
    comp = getComp(A[i])
    j = bisect_left(A, comp)
    while True:
        if A[j] != comp:
            break
        if i == j or not avail[j]:
            j += 1
            continue
        avail[i] = False
        avail[j] = False
        count += 1
        break

print(count)


Fixed submission:
# from math import log2
from math import log
from bisect import bisect_left


def log2(x):
    return log(x, 2)


def getComp(n):
    return (1 << (1 + int(log2(n)))) - n


N = int(input())
A = [int(s) for s in input().split()]
A.sort()
B = []
C = []
i = 0
while i < len(A):
    j = i
    count = 1
    while i+1 < len(A) and A[j] == A[i+1]:
        count += 1
        i += 1
    B.append(A[j])
    C.append(count)
    i += 1

count = 0
i = len(B) - 1
while i >= 0:
    comp = getComp(B[i])
    j = bisect_left(B, comp)
    if i == j and C[i] < 2:
        i -= 1
        continue
    if B[j] != comp:
        i -= 1
        continue
    if not C[i] or not C[j]:
        i -= 1
        continue
    C[i] -= 1
    C[j] -= 1
    count += 1

print(count)