Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
from sys import stdin
import numpy as np

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = np.array(ds_in())
A_list.sort()
EPSILON = 10**(-6)

cand_A = 2 ** (np.log2(A_list + EPSILON).astype(int) + 1) - A_list
idx = np.searchsorted(A_list, cand_A)
flag = np.zeros(N, dtype=int)

ans = 0
for i in range(N-1, -1, -1):
    if flag[i]:
        continue
    if A_list[idx[i]] == cand_A[i]:
        cand_idx = idx[i]
        while (cand_idx < i) and (A_list[cand_idx] == cand_A[i]):
            if not flag[cand_idx]:
                ans += 1
                flag[cand_idx] = 1
                break
            cand_idx += 1

print(ans)



Fixed submission:
# -*- coding: utf-8 -*-
from sys import stdin
import numpy as np
from collections import Counter

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = np.array(ds_in())
A_list.sort()
EPSILON = 10**(-6)

cand_A = 2 ** (np.log2(A_list + EPSILON).astype(int) + 1) - A_list
idx = np.searchsorted(A_list, cand_A)
A_count = dict(Counter(A_list))

ans = 0
for i in range(N-1, -1, -1):
    if A_count[A_list[i]] <= 0:
        continue
    A_count[A_list[i]] -= 1
    if (A_list[idx[i]] == cand_A[i]) and (A_count[cand_A[i]] > 0):
        ans += 1
        A_count[cand_A[i]] -= 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
from sys import stdin
from bisect import bisect_left

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = ds_in()
A_list.sort()

ans = 0
while N > 1:
    max_a = A_list.pop()
    N -= 1
    order = len(bin(max_a)) - 3
    if max_a == (1 << order) == A_list[-1]:
        del A_list[-1]
        ans += 1
        N -= 1
    else:
        cand = (1 << (order+1)) - max_a
        idx = bisect_left(A_list, cand)
        if (idx < N) and (cand == A_list[idx]):
            del A_list[idx]
            ans += 1
            N -= 1
print(ans)


Fixed submission:
# -*- coding: utf-8 -*-
from sys import stdin
import numpy as np
from collections import Counter

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = np.array(ds_in())
A_list.sort()
EPSILON = 10**(-6)

cand_A = 2 ** (np.log2(A_list + EPSILON).astype(int) + 1) - A_list
idx = np.searchsorted(A_list, cand_A)
A_count = dict(Counter(A_list))

ans = 0
for i in range(N-1, -1, -1):
    if A_count[A_list[i]] <= 0:
        continue
    A_count[A_list[i]] -= 1
    if (A_list[idx[i]] == cand_A[i]) and (A_count[cand_A[i]] > 0):
        ans += 1
        A_count[cand_A[i]] -= 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
from sys import stdin
from bisect import bisect_left

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = ds_in()
A_list.sort()

ans = 0
while len(A_list) > 1:
    max_a = A_list.pop()
    order = len(bin(max_a)) - 3
    if max_a == (1 << order) == A_list[-1]:
        del A_list[-1]
        ans += 1
    else:
        cand = (1 << (order+1)) - max_a
        idx = bisect_left(A_list, cand)
        if (idx < len(A_list)) and (cand == A_list[idx]):
            del A_list[idx]
            ans += 1

print(ans)


Fixed submission:
# -*- coding: utf-8 -*-
from sys import stdin
import numpy as np
from collections import Counter

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = np.array(ds_in())
A_list.sort()
EPSILON = 10**(-6)

cand_A = 2 ** (np.log2(A_list + EPSILON).astype(int) + 1) - A_list
idx = np.searchsorted(A_list, cand_A)
A_count = dict(Counter(A_list))

ans = 0
for i in range(N-1, -1, -1):
    if A_count[A_list[i]] <= 0:
        continue
    A_count[A_list[i]] -= 1
    if (A_list[idx[i]] == cand_A[i]) and (A_count[cand_A[i]] > 0):
        ans += 1
        A_count[cand_A[i]] -= 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
from sys import stdin
from bisect import bisect_left

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = ds_in()
A_list.sort()

ans = 0
while len(A_list) > 1:
    max_a = A_list.pop()
    binary = bin(max_a)
    cand = (1 << len(binary[2:])) - max_a
    if cand == 0:
        if max_a == A_list[-1]:
            del A_list[-1]
            ans += 1
    else:
        idx = bisect_left(A_list, cand)
        if (idx < len(A_list)) and (cand == A_list[idx]):
            del A_list[idx]
            ans += 1

print(ans)


Fixed submission:
# -*- coding: utf-8 -*-
from sys import stdin
import numpy as np
from collections import Counter

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = np.array(ds_in())
A_list.sort()
EPSILON = 10**(-6)

cand_A = 2 ** (np.log2(A_list + EPSILON).astype(int) + 1) - A_list
idx = np.searchsorted(A_list, cand_A)
A_count = dict(Counter(A_list))

ans = 0
for i in range(N-1, -1, -1):
    if A_count[A_list[i]] <= 0:
        continue
    A_count[A_list[i]] -= 1
    if (A_list[idx[i]] == cand_A[i]) and (A_count[cand_A[i]] > 0):
        ans += 1
        A_count[cand_A[i]] -= 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
from sys import stdin
from bisect import bisect_left

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = ds_in()
A_list.sort()

ans = 0
while len(A_list) > 1:
    max_a = A_list.pop()
    binary = bin(max_a)
    cand = 2 ** len(binary[2:]) - max_a
    if cand == 0:
        if max_a == A_list[-1]:
            A_list.pop()
            ans += 1
    else:
        idx = bisect_left(A_list, cand)
        if idx < len(A_list) and cand == A_list[idx]:
            A_list.pop(idx)
            ans += 1

print(ans)


Fixed submission:
# -*- coding: utf-8 -*-
from sys import stdin
import numpy as np
from collections import Counter

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = np.array(ds_in())
A_list.sort()
EPSILON = 10**(-6)

cand_A = 2 ** (np.log2(A_list + EPSILON).astype(int) + 1) - A_list
idx = np.searchsorted(A_list, cand_A)
A_count = dict(Counter(A_list))

ans = 0
for i in range(N-1, -1, -1):
    if A_count[A_list[i]] <= 0:
        continue
    A_count[A_list[i]] -= 1
    if (A_list[idx[i]] == cand_A[i]) and (A_count[cand_A[i]] > 0):
        ans += 1
        A_count[cand_A[i]] -= 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
from sys import stdin
from bisect import bisect_left

s_in = lambda: stdin.readline()[:-1]  # s = s_in()
d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = ds_in()

A_list.sort()

ans = 0
while len(A_list) > 1:
    max_a = A_list.pop()
    if bin(max_a)[3:].find('1') == -1:
        if max_a == A_list[-1]:
            A_list.pop()
            ans += 1
    else:
        cand = 2 ** len(bin(max_a)[2:]) - max_a
        idx = bisect_left(A_list, cand)
        if idx < len(A_list) and cand == A_list[idx]:
            A_list.pop(idx)
            ans += 1

print(ans)


Fixed submission:
# -*- coding: utf-8 -*-
from sys import stdin
import numpy as np
from collections import Counter

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = np.array(ds_in())
A_list.sort()
EPSILON = 10**(-6)

cand_A = 2 ** (np.log2(A_list + EPSILON).astype(int) + 1) - A_list
idx = np.searchsorted(A_list, cand_A)
A_count = dict(Counter(A_list))

ans = 0
for i in range(N-1, -1, -1):
    if A_count[A_list[i]] <= 0:
        continue
    A_count[A_list[i]] -= 1
    if (A_list[idx[i]] == cand_A[i]) and (A_count[cand_A[i]] > 0):
        ans += 1
        A_count[cand_A[i]] -= 1

print(ans)

Buggy python submission (verdict: Runtime Error):
# -*- coding: utf-8 -*-
from sys import stdin
from bisect import bisect_left

s_in = lambda: stdin.readline()[:-1]  # s = s_in()
d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = ds_in()

A_list.sort()

ans = 0
while len(A_list) > 1:
    max_a = A_list.pop()
    if bin(max_a)[3:].find('1') == -1:
        if max_a == A_list[-1]:
            A_list.pop()
            ans += 1
    else:
        cand = 2 ** len(bin(max_a)[2:]) - max_a
        idx = bisect_left(A_list, cand)
        if cand == A_list[idx]:
            A_list.pop(idx)
            ans += 1

print(ans)


Fixed submission:
# -*- coding: utf-8 -*-
from sys import stdin
import numpy as np
from collections import Counter

d_in = lambda: int(stdin.readline())  # N = d_in()
ds_in = lambda: list(map(int, stdin.readline().split()))  # List = ds_in()

N = d_in()
A_list = np.array(ds_in())
A_list.sort()
EPSILON = 10**(-6)

cand_A = 2 ** (np.log2(A_list + EPSILON).astype(int) + 1) - A_list
idx = np.searchsorted(A_list, cand_A)
A_count = dict(Counter(A_list))

ans = 0
for i in range(N-1, -1, -1):
    if A_count[A_list[i]] <= 0:
        continue
    A_count[A_list[i]] -= 1
    if (A_list[idx[i]] == cand_A[i]) and (A_count[cand_A[i]] > 0):
        ans += 1
        A_count[cand_A[i]] -= 1

print(ans)