Buggy python submission (verdict: Time Limit Exceeded):
import queue
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
R=[0 for i in range(N)]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=queue.Queue()
    D[A[i]].put(i)
ans=0
for i in range(N):
    if R[i]==1:
        continue
    if B[i]==2*A[i]:
        if A[i] in D:
            flag=0
            x=0;y=0
            if not(D[A[i]].empty()):
                x=D[A[i]].get()
                flag=1
            if flag==1 and not(D[A[i]].empty()):
                y=D[A[i]].get()
                flag=2
            if flag==2:
                R[x]=1
                R[y]=1
                ans+=1
    else:
        if (B[i]-A[i]) in D:
            if not(D[B[i]-A[i]].empty()):
                it=D[A[i]].get()
                j=D[B[i]-A[i]].get()
                R[i]=1
                R[j]=1
                ans+=1
print(ans)



Fixed submission:
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=1
    else:
        D[A[i]]+=1
ans=0
for i in range(N):
    if D[A[i]]<=0:
        continue
    if B[i]==2*A[i]:
        if D[A[i]]>=2:
            D[A[i]]-=2
            ans+=1
    else:
        if (B[i]-A[i]) in D:
            if D[B[i]-A[i]]!=0:
                D[A[i]]-=1
                D[B[i]-A[i]]-=1
                ans+=1
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
R=[0 for i in range(N)]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=queue.Queue()
    D[A[i]].put(i)
ans=0
for i in range(N):
    if R[i]==1:
        continue
    if (B[i]-A[i]) in D:
        itmp=D[A[i]].get()
        if not(D[B[i]-A[i]].empty()):
            j=D[B[i]-A[i]].get()
            R[i]=1
            R[j]=1
            #print(i,j)
            ans+=1
print(ans)



Fixed submission:
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=1
    else:
        D[A[i]]+=1
ans=0
for i in range(N):
    if D[A[i]]<=0:
        continue
    if B[i]==2*A[i]:
        if D[A[i]]>=2:
            D[A[i]]-=2
            ans+=1
    else:
        if (B[i]-A[i]) in D:
            if D[B[i]-A[i]]!=0:
                D[A[i]]-=1
                D[B[i]-A[i]]-=1
                ans+=1
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
R=[0 for i in range(N)]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=queue.Queue()
    D[A[i]].put(i)
ans=0
for i in range(N):
    if R[i]==1:
        continue
    if (B[i]-A[i]) in D:
        flag=1
        if not(D[B[i]-A[i]].empty()):
            itmp=D[A[i]].get()
            j=D[B[i]-A[i]].get()
            #R[i]=1
            R[j]=1
            #print(i,j)
            ans+=1
print(ans)



Fixed submission:
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=1
    else:
        D[A[i]]+=1
ans=0
for i in range(N):
    if D[A[i]]<=0:
        continue
    if B[i]==2*A[i]:
        if D[A[i]]>=2:
            D[A[i]]-=2
            ans+=1
    else:
        if (B[i]-A[i]) in D:
            if D[B[i]-A[i]]!=0:
                D[A[i]]-=1
                D[B[i]-A[i]]-=1
                ans+=1
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
R=[0 for i in range(N)]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=queue.Queue()
    D[A[i]].put(i)
ans=0
for i in range(N):
    if R[i]==1:
        continue
    if (B[i]-A[i]) in D:
        flag=1
        if not(D[B[i]-A[i]].empty()):
            j=D[B[i]-A[i]].get()
            if i!=j:
                R[i]=1
                R[j]=1
                #print(i,j)
                ans+=1
            else:
                if not(D[B[i]-A[i]].empty()):
                    j=D[B[i]-A[i]].get()
                    R[i]=1
                    R[j]=1
                    #print(i,j)
                    ans+=1
print(ans)



Fixed submission:
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=1
    else:
        D[A[i]]+=1
ans=0
for i in range(N):
    if D[A[i]]<=0:
        continue
    if B[i]==2*A[i]:
        if D[A[i]]>=2:
            D[A[i]]-=2
            ans+=1
    else:
        if (B[i]-A[i]) in D:
            if D[B[i]-A[i]]!=0:
                D[A[i]]-=1
                D[B[i]-A[i]]-=1
                ans+=1
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
R=[0 for i in range(N)]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=queue.Queue()
    D[A[i]].put(i)
ans=0
for i in range(N):
    if R[i]==1:
        continue
    if (B[i]-A[i]) in D:
        flag=1
        if not(D[B[i]-A[i]].empty()):
            j=D[B[i]-A[i]].get()
            if i!=j:
                R[i]=1
                R[j]=1
                #print(i,j)
                ans+=1
            else:
                if not(D[B[i]-A[i]].empty()):
                    j=D[B[i]-A[i]].get()
                    R[i]=1
                    R[j]=1
                    #print(i,j)
                    ans+=1
print(ans)



Fixed submission:
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)
B=[2**(len(bin(i))-2) for i in A]
D=dict()
for i in range(N):
    if not(A[i] in D):
        D[A[i]]=1
    else:
        D[A[i]]+=1
ans=0
for i in range(N):
    if D[A[i]]<=0:
        continue
    if B[i]==2*A[i]:
        if D[A[i]]>=2:
            D[A[i]]-=2
            ans+=1
    else:
        if (B[i]-A[i]) in D:
            if D[B[i]-A[i]]!=0:
                D[A[i]]-=1
                D[B[i]-A[i]]-=1
                ans+=1
print(ans)