Buggy python submission (verdict: Time Limit Exceeded):
def main():
    from collections import Counter
    import sys
    input = sys.stdin.buffer.readline

    _ = int(input())
    A = [int(i) for i in input().split()]

    ans = 0
    c = Counter(A)
    B = sorted(c.keys(), reverse=True)

    for b in B:
        if c[b] == 0:
            continue
        a = (2 ** b.bit_length()) - b
        if a == b:
            cur = c[b]//2
        else:
            if a in c.keys():
                cur = min(c[a], c[b])
            else:
                cur = 0
        ans += cur
        # c[b] -= cur
        c[a] -= cur

    print(ans)


if __name__ == '__main__':
    main()


Fixed submission:
from collections import Counter

n = int(input())
A = [int(i) for i in input().split()]

A.sort(reverse=True)
C = Counter(A)
m = 1 << 30
ans = 0

for a in A:
    if C[a] <= 0:
        continue
    C[a] -= 1
    while m > a * 2:
        m >>= 1
    v = m - a
    if v in C and C[v] > 0:
        C[v] -= 1
        ans += 1

print(ans)

Buggy python submission (verdict: Runtime Error):
def main():
    from collections import Counter
    import sys
    input = sys.stdin.buffer.readline

    _ = int(input())
    A = [int(i) for i in input().split()]

    ans = 0
    c = Counter(A)
    B = sorted(c.keys(), reverse=True)

    for b in B:
        if c[b] == 0:
            continue
        a = (2 ** b.bit_length()) - b
        if a == b:
            cur = c[b]//2
        else:
            if a in C:
                cur = min(c[a], c[b])
            else:
                cur = 0
        ans += cur
        # c[b] -= cur
        c[a] -= cur

    print(ans)


if __name__ == '__main__':
    main()


Fixed submission:
from collections import Counter

n = int(input())
A = [int(i) for i in input().split()]

A.sort(reverse=True)
C = Counter(A)
m = 1 << 30
ans = 0

for a in A:
    if C[a] <= 0:
        continue
    C[a] -= 1
    while m > a * 2:
        m >>= 1
    v = m - a
    if v in C and C[v] > 0:
        C[v] -= 1
        ans += 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
A = [int(i) for i in input().split()]

A.sort()
m = 1 << 30
used = [False] * n
ans = 0

def search(ok, ng, n):
    if abs(ok-ng) <= 1:
            return ok
    mid = (ok+ng) // 2
    if A[mid] < n or (A[mid] == n and used[mid]):
        return search(mid, ng, n)
    else:
        return search(ok, mid, n)

for i in range(30):
    for j in range(n):
        if A[j] >= m:
            break
        if used[j]:
            continue
        a = search(-1, n, m - A[j]) + 1
        if a >= n:
            continue
        if A[a] == m - A[j]:
            if a == j:
                a += 1
                if a >= n or not A[a] == A[j]:
                    continue
            used[a] = True
            used[j] = True
            ans += 1
    m >>= 1

print(ans)

Fixed submission:
from collections import Counter

n = int(input())
A = [int(i) for i in input().split()]

A.sort(reverse=True)
C = Counter(A)
m = 1 << 30
ans = 0

for a in A:
    if C[a] <= 0:
        continue
    C[a] -= 1
    while m > a * 2:
        m >>= 1
    v = m - a
    if v in C and C[v] > 0:
        C[v] -= 1
        ans += 1

print(ans)

Buggy python submission (verdict: Runtime Error):
n = int(input())
A = [int(i) for i in input().split()]

A.sort()
m = 1 << 30
used = [False] * n
ans = 0

def search(ok, ng, n):
    if abs(ok-ng) <= 1:
            return ok
    mid = (ok+ng) // 2
    if A[mid] < n or (A[mid] == n and used[mid]):
        return search(mid, ng, n)
    else:
        return search(ok, mid, n)

for i in range(30):
    for j in range(n):
        if A[j] >= m:
            break
        if used[j]:
            cotinue
        a = search(-1, n, m - A[j]) + 1
        if a >= n:
            continue
        if A[a] == m - A[j]:
            if a == j:
                a += 1
                if a >= n or not A[a] == A[j]:
                    continue
            used[a] = True
            used[j] = True
            ans += 1
    m >>= 1

print(ans)



Fixed submission:
from collections import Counter

n = int(input())
A = [int(i) for i in input().split()]

A.sort(reverse=True)
C = Counter(A)
m = 1 << 30
ans = 0

for a in A:
    if C[a] <= 0:
        continue
    C[a] -= 1
    while m > a * 2:
        m >>= 1
    v = m - a
    if v in C and C[v] > 0:
        C[v] -= 1
        ans += 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
A = [int(i) for i in input().split()]

A.sort()
m = 1 << 30
used = [False] * n
ans = 0

def search(ok, ng, n):
    if abs(ok-ng) <= 1:
            return ok
    mid = (ok+ng) // 2
    if A[mid] < n or (A[mid] == n and used[mid]):
        return search(mid, ng, n)
    else:
        return search(ok, mid, n)

for i in range(30):
    for j in range(n):
        if used[j] or A[j] >= m:
            continue
        a = search(-1, n, m - A[j]) + 1
        if a >= n:
            continue
        if A[a] == m - A[j]:
            if a == j:
                a += 1
                if a >= n or not A[a] == A[j]:
                    continue
            used[a] = True
            used[j] = True
            ans += 1
    m >>= 1

print(ans)

Fixed submission:
from collections import Counter

n = int(input())
A = [int(i) for i in input().split()]

A.sort(reverse=True)
C = Counter(A)
m = 1 << 30
ans = 0

for a in A:
    if C[a] <= 0:
        continue
    C[a] -= 1
    while m > a * 2:
        m >>= 1
    v = m - a
    if v in C and C[v] > 0:
        C[v] -= 1
        ans += 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
A = [int(i) for i in input().split()]

A.sort()
m = 2 ** 31
used = set()
ans = 0

def search(ok, ng, n):
    if abs(ok-ng) <= 1:
            return ok
    mid = (ok+ng) // 2
    if A[mid] < n or (A[mid] == n and mid in used):
        return search(mid, ng, n)
    else:
        return search(ok, mid, n)

for i in range(30):
    m //= 2
    for j in range(n):
        if j in used or A[j] >= m:
            continue
        a = search(-1, n, m - A[j]) + 1
        if a >= n:
            continue
        if A[a] == m - A[j]:
            if a == j:
                a += 1
                if a >= n or not A[a] == A[j]:
                    continue
            used.add(a)
            used.add(j)
            ans += 1

ans2 = 0
used = set()
m = 1

for i in range(31):
    m *= 2
    for j in range(n):
        if j in used or A[j] >= m:
            continue
        a = search(-1, n, m - A[j]) + 1
        if a >= n:
            continue
        if A[a] == m - A[j]:
            if a == j:
                a += 1
                if a >= n or not A[a] == A[j]:
                    continue
            used.add(a)
            used.add(j)
            ans2 += 1

print(max(ans, ans2))

Fixed submission:
from collections import Counter

n = int(input())
A = [int(i) for i in input().split()]

A.sort(reverse=True)
C = Counter(A)
m = 1 << 30
ans = 0

for a in A:
    if C[a] <= 0:
        continue
    C[a] -= 1
    while m > a * 2:
        m >>= 1
    v = m - a
    if v in C and C[v] > 0:
        C[v] -= 1
        ans += 1

print(ans)

Buggy python submission (verdict: Runtime Error):
n = int(input())
A = [int(i) for i in input().split()]

A.sort()
m = 2 ** 30
used = set()
ans = 0

def search(ok, ng, n):
    if abs(ok-ng) <= 1:
            return ok
    mid = (ok+ng) // 2
    if A[mid] < n or (A[mid] == n and mid in used):
        return search(mid, ng, n)
    else:
        return search(ok, mid, n)

for i in range(30):
    m //= 2
    for j in range(n):
        if j in used or A[j] >= m:
            continue
        a = search(-1, n, m - A[j]) + 1
        if a >= n:
            continue
        if A[a] == m - A[j]:
            if a == j:
                if not A[a+1] == A[j]:
                    continue
                a += 1
            used.add(a)
            used.add(j)
            ans += 1

ans2 = 0
used = set()

for i in range(30):
    m *= 2
    for j in range(n):
        if j in used or A[j] >= m:
            continue
        a = search(-1, n, m - A[j]) + 1
        if a >= n:
            continue
        if A[a] == m - A[j]:
            if a == j:
                if not A[a+1] == A[j]:
                    continue
                a += 1
            used.add(a)
            used.add(j)
            ans2 += 1

print(max(ans, ans2))

Fixed submission:
from collections import Counter

n = int(input())
A = [int(i) for i in input().split()]

A.sort(reverse=True)
C = Counter(A)
m = 1 << 30
ans = 0

for a in A:
    if C[a] <= 0:
        continue
    C[a] -= 1
    while m > a * 2:
        m >>= 1
    v = m - a
    if v in C and C[v] > 0:
        C[v] -= 1
        ans += 1

print(ans)

Buggy python submission (verdict: Runtime Error):
n = int(input())
A = [int(i) for i in input().split()]

A.sort()
m = 2 ** 31
used = set()
ans = 0

def search(ok, ng, n):
    if abs(ok-ng) <= 1:
            return ok
    mid = (ok+ng) // 2
    if A[mid] < n or (A[mid] == n and mid in used):
        return search(mid, ng, n)
    else:
        return search(ok, mid, n)

for i in range(30):
    m //= 2
    for j in range(n):
        if j in used or A[j] >= m:
            continue
        a = search(-1, n, m - A[j]) + 1
        if a >= n:
            continue
        if A[a] == m - A[j]:
            if a == j:
                if not A[a+1] == A[j]:
                    continue
                a += 1
            used.add(a)
            used.add(j)
            ans += 1

print(ans)

Fixed submission:
from collections import Counter

n = int(input())
A = [int(i) for i in input().split()]

A.sort(reverse=True)
C = Counter(A)
m = 1 << 30
ans = 0

for a in A:
    if C[a] <= 0:
        continue
    C[a] -= 1
    while m > a * 2:
        m >>= 1
    v = m - a
    if v in C and C[v] > 0:
        C[v] -= 1
        ans += 1

print(ans)