Buggy python submission (verdict: Time Limit Exceeded):
from bisect import bisect_left
N = int(input())
A = sorted(list(map(int,input().split())))
cnt = 0
hist = [0 for _ in range(N)]
for i in range(N-1,0,-1):
    if hist[i]==0:
        a = A[i]
        k = 0
        while 2**k<=a:
            k += 1
        b = 2**k-a
        ind = bisect_left(A,b)
        if ind<i and A[ind]==b and hist[ind]==0:
            hist[i]=1
            hist[ind]=1
            cnt += 1
        elif ind<i and A[ind]==b and hist[ind]==1:
            ind += 1
            while A[ind]==b and ind<i:
                if hist[ind]==0:
                    hist[i]=1
                    hist[ind]=1
                    cnt += 1
                    break
                ind += 1
print(cnt)

Fixed submission:
from bisect import bisect_left
N = int(input())
A = sorted(list(map(int,input().split())))
A = [[A[i],0] for i in range(N)]
cnt = 0
for i in range(N-1,0,-1):
    if A[i][1]==0:
        a = A[i][0]
        A[i][1]=1
        k = 0
        while 2**k<=a:
            k += 1
        b = 2**k-a
        ind = bisect_left(A,[b,1])
        ind -= 1
        if ind<i and A[ind]==[b,0]:
            A[ind][1]=1
            cnt += 1
print(cnt)

Buggy python submission (verdict: Time Limit Exceeded):
from bisect import bisect_left
N = int(input())
A = sorted(list(map(int,input().split())))
cnt = 0
hist = [0 for _ in range(N)]
for i in range(N-1,0,-1):
    if hist[i]==0:
        a = A[i]
        k = 0
        while 2**k<=a:
            k += 1
        b = 2**k-a
        ind = bisect_left(A[:i],b)
        if ind<i and hist[ind]==0:
            hist[i]=1
            hist[ind]=1
            cnt += 1
        elif ind<i and hist[ind]==1:
            ind += 1
            while A[ind]==b and ind<i:
                if hist[ind]==0:
                    hist[i]=1
                    hist[ind]=1
                    cnt += 1
                    break
                ind += 1
print(cnt)

Fixed submission:
from bisect import bisect_left
N = int(input())
A = sorted(list(map(int,input().split())))
A = [[A[i],0] for i in range(N)]
cnt = 0
for i in range(N-1,0,-1):
    if A[i][1]==0:
        a = A[i][0]
        A[i][1]=1
        k = 0
        while 2**k<=a:
            k += 1
        b = 2**k-a
        ind = bisect_left(A,[b,1])
        ind -= 1
        if ind<i and A[ind]==[b,0]:
            A[ind][1]=1
            cnt += 1
print(cnt)

Buggy python submission (verdict: Time Limit Exceeded):
from bisect import bisect_left
N = int(input())
A = sorted(list(map(int,input().split())))
cnt = 0
hist = [0 for _ in range(N)]
for i in range(N-1,0,-1):
    if hist[i]==0:
        a = A[i]
        k = 0
        while 2**k<=a:
            k += 1
        b = 2**k-a
        ind = bisect_left(A[:i],b)
        if ind<i and hist[ind]==0:
            hist[i]=1
            hist[ind]=1
            cnt += 1
        elif ind<i and hist[ind]==1:
            ind += 1
            while A[ind]==b:
                if hist[ind]==0:
                    hist[i]=1
                    hist[ind]=1
                    cnt += 1
                    break
print(cnt)

Fixed submission:
from bisect import bisect_left
N = int(input())
A = sorted(list(map(int,input().split())))
A = [[A[i],0] for i in range(N)]
cnt = 0
for i in range(N-1,0,-1):
    if A[i][1]==0:
        a = A[i][0]
        A[i][1]=1
        k = 0
        while 2**k<=a:
            k += 1
        b = 2**k-a
        ind = bisect_left(A,[b,1])
        ind -= 1
        if ind<i and A[ind]==[b,0]:
            A[ind][1]=1
            cnt += 1
print(cnt)

Buggy python submission (verdict: Runtime Error):
from bisect import bisect_left
N = int(input())
A = sorted(list(map(int,input().split())))
G = {}
for i in range(N-1,0,-1):
    a = A[i]
    kmin = 0
    while 2**kmin<=a:
        kmin += 1
    kmax = 0
    while 2**kmax<=2*a:
        kmax += 1
    for k in range(kmin,kmax):
        b = 2**k-a
        ind = bisect_left(A[:i],b)
        if A[ind]==b and ind<i:
            if 2**k not in G:
                G[2**k] = []
            G[2**k].append((i,ind))
            ind += 1
            while A[ind]==b:
                G[2**k].append((i,ind))
                ind += 1
C = sorted([[a,len(G[a])] for a in G],key=lambda x:x[1],reverse=True)
hist = [0 for _ in range(N)]
cnt = 0
for c in C:
    a,_ = c
    for x in G[a]:
        i,j = x
        if hist[i]==0 and hist[j]==0:
            cnt += 1
            hist[i] = 1
            hist[j] = 1
print(cnt)

Fixed submission:
from bisect import bisect_left
N = int(input())
A = sorted(list(map(int,input().split())))
A = [[A[i],0] for i in range(N)]
cnt = 0
for i in range(N-1,0,-1):
    if A[i][1]==0:
        a = A[i][0]
        A[i][1]=1
        k = 0
        while 2**k<=a:
            k += 1
        b = 2**k-a
        ind = bisect_left(A,[b,1])
        ind -= 1
        if ind<i and A[ind]==[b,0]:
            A[ind][1]=1
            cnt += 1
print(cnt)