Buggy python submission (verdict: Runtime Error):
from collections import Counter
n = int(input())
A = sorted(list(map(int, input().split())))[-1::-1]
c = Counter(A)
ans = 0
for a in A:
    b = (1<<m.bit_length()) - a
    if a == b and c[a] > 1:
        c[a] -= 2
        ans += 1
    elif a != b and c[a] > 0 and c[b] > 0:
        c[a] -= 1
        c[b] -= 1
        ans += 1
print(ans)


Fixed submission:
from collections import Counter
n = int(input())
A = sorted(list(map(int, input().split())))[-1::-1]
c = Counter(A)
ans = 0
for a in A:
    b = (1<<a.bit_length()) - a
    if a == b and c[a] > 1:
        c[a] -= 2
        ans += 1
    elif a != b and c[a] > 0 and c[b] > 0:
        c[a] -= 1
        c[b] -= 1
        ans += 1
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from math import log2
n = int(input())
a = sorted(list(map(int, input().split())))
ans = 0
while a:
    m = a.pop()
    k = (1<<m.bit_length()) - m
    if k in a:
        a.remove(k)
        ans += 1
print(ans)


Fixed submission:
from collections import Counter
n = int(input())
A = sorted(list(map(int, input().split())))[-1::-1]
c = Counter(A)
ans = 0
for a in A:
    b = (1<<a.bit_length()) - a
    if a == b and c[a] > 1:
        c[a] -= 2
        ans += 1
    elif a != b and c[a] > 0 and c[b] > 0:
        c[a] -= 1
        c[b] -= 1
        ans += 1
print(ans)

Buggy python submission (verdict: Runtime Error):
from math import log2
n = int(input())
a = sorted(list(map(int, input().split())))
ans = 0
while a:
    m = a.pop()
    k = (1<<m.bit_length()) - m
    if k in a:
        a.remove(k)
        ans += 1
print(ans)


Fixed submission:
from collections import Counter
n = int(input())
A = sorted(list(map(int, input().split())))[-1::-1]
c = Counter(A)
ans = 0
for a in A:
    b = (1<<a.bit_length()) - a
    if a == b and c[a] > 1:
        c[a] -= 2
        ans += 1
    elif a != b and c[a] > 0 and c[b] > 0:
        c[a] -= 1
        c[b] -= 1
        ans += 1
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from math import log2
n = int(input())
a = sorted(list(map(int, input().split())))
ans = 0
while a:
    m = a.pop()
    for i in range(int(log2(m))+2):
        k = 2**i - m
        if k in a:
            a.remove(k)
            ans += 1
print(ans)


Fixed submission:
from collections import Counter
n = int(input())
A = sorted(list(map(int, input().split())))[-1::-1]
c = Counter(A)
ans = 0
for a in A:
    b = (1<<a.bit_length()) - a
    if a == b and c[a] > 1:
        c[a] -= 2
        ans += 1
    elif a != b and c[a] > 0 and c[b] > 0:
        c[a] -= 1
        c[b] -= 1
        ans += 1
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = sorted(list(map(int, input().split())))
ans = 0
while a:
    m = a.pop()
    for i in range(31):
        k = 2**i - m
        if k in a:
            a.remove(k)
            ans += 1
print(ans)


Fixed submission:
from collections import Counter
n = int(input())
A = sorted(list(map(int, input().split())))[-1::-1]
c = Counter(A)
ans = 0
for a in A:
    b = (1<<a.bit_length()) - a
    if a == b and c[a] > 1:
        c[a] -= 2
        ans += 1
    elif a != b and c[a] > 0 and c[b] > 0:
        c[a] -= 1
        c[b] -= 1
        ans += 1
print(ans)