Buggy python submission (verdict: Runtime Error):
import math

N = int(input())
a = sorted(list(map(int,input().split())))

count = 0



while(a!=[]):
    temp = a[-1]
    a.pop(-1)
    b=2**math.floor(math.log2(temp))
    if a ==[]:
        break
    if 2*b-temp > 0:
        count += 1
        a.pop(a.index(2*b-temp))
    
print(count)



Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)

Buggy python submission (verdict: Time Limit Exceeded):
import math

N = int(input())
a = sorted(list(map(int,input().split())))

count = 0



while(a!=[]):
    temp = a[-1]
    a.pop(-1)
    b=2**math.floor(math.log2(temp))
    if a ==[]:
        break
    if 2*b-temp in a:
        count += 1
        a.pop(a.index(2*b-temp))
    
print(count)



Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)

Buggy python submission (verdict: Time Limit Exceeded):
import math

N = int(input())
a = sorted(list(map(int,input().split())))

count = 0
while(a!=[]):
    temp = a[-1]
    a.pop(-1)
    b=2**math.floor(math.log2(temp))
    if a ==[]:
        break
    if 2*b-temp in a:
        count += 1
        a.pop(a.index(2*b-temp))
    
print(count)



Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)

Buggy python submission (verdict: Time Limit Exceeded):
import math

N = int(input())
a = list(map(int,input().split()))

count = 0
a.sort()

while(a!=[]):
    temp = a[-1]
    a.pop(-1)
    b=2**math.floor(math.log2(temp))
    if a ==[]:
        break
    if 2*b-temp in a:
        count += 1
        a.pop(a.index(2*b-temp))
    
    
print(count)



Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)

Buggy python submission (verdict: Time Limit Exceeded):
import math

N = int(input())
a = list(map(int,input().split()))

count = 0
a.sort()
a.reverse()

while(a!=[]):
    temp = a[0]
    a.pop(0)
    b=2**math.floor(math.log2(temp))
    if a ==[]:
        break
    if 2*b-temp in a:
        count += 1
        a.pop(a.index(2*b-temp))
    
    


print(count)

Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)

Buggy python submission (verdict: Time Limit Exceeded):
import math

N = int(input())
a = list(map(int,input().split()))
a_odds = []
a_even = []

for i in range(N):
    if a[i]%2 != 0:
        a_odds.append(a[i])
    else:
        a_even.append(a[i])

a_odds.sort()
a_odds.reverse()
a_even.sort()
a_even.reverse()

count = 0
alist = []
num= 0
if a_odds!=[] and a_even!=[]:
    num = max(a_odds[0],a_even[0])
elif a_odds ==[]:
    num= a_even[0]
elif a_even == []:
    num = a_odds[0]
    
for i in range(math.floor(math.log2(num))+1,0,-1):
    alist.append(2**i)


while(a_odds!=[]):
    temp = a_odds[0]
    a_odds.pop(0)
    b=2**math.floor(math.log2(temp))
    if a_odds ==[]:
        break
    if 2*b-temp in a_odds:
        count += 1
        a_odds.pop(a_odds.index(2*b-temp))
    
    
while(a_even!=[]):
    temp = a_even[0]
    a_even.pop(0)
    if a_even==[]:
        break
    for i in alist:
        if temp > i:
            break
        if (i-temp) in a_even:
            count += 1
            a_even.pop(a_even.index(i-temp))
            break
    

print(count)







Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)

Buggy python submission (verdict: Time Limit Exceeded):
import math

N = int(input())
a = list(map(int,input().split()))
a_odds = []
a_even = []

for i in range(N):
    if a[i]%2 != 0:
        a_odds.append(a[i])
    else:
        a_even.append(a[i])

a_odds.sort()
a_odds.reverse()
a_even.sort()
a_even.reverse()

count = 0
alist = []
num= 0
if a_odds!=[] and a_even!=[]:
    num = max(a_odds[0],a_even[0])
elif a_odds ==[]:
    num= a_even[0]
elif a_even == []:
    num = a_odds[0]
    
for i in range(round(math.log2(num))+1,0,-1):
    alist.append(2**i)


while(a_odds!=[]):
    temp = a_odds[0]
    a_odds.pop(0)
    if a_odds ==[]:
        break
    for i in alist:
        b = i-temp
        if (i-temp) in a_odds:
            count += 1
            a_odds.pop(a_odds.index(i-temp))
            break
    
    
while(a_even!=[]):
    temp = a_even[0]
    a_even.pop(0)
    if a_even==[]:
        break
    for i in alist:
        if (i-temp) in a_even:
            count += 1
            a_even.pop(a_even.index(i-temp))
            break
    

print(count)

Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)

Buggy python submission (verdict: Time Limit Exceeded):
import math

N = int(input())
a = list(map(int,input().split()))
a_odds = []
a_even = []

for i in range(N):
    if a[i]%2 != 0:
        a_odds.append(a[i])
    else:
        a_even.append(a[i])

a_odds.sort()
a_odds.reverse()
a_even.sort()
a_even.reverse()

count = 0
alist = []
num= 0
if a_odds!=[] and a_even!=[]:
    num = max(a_odds[0],a_even[0])
elif a_odds ==[]:
    num= a_even[0]
elif a_even == []:
    num = a_odds[0]
    
for i in range(round(math.log2(num))+1,0,-1):
    alist.append(2**i)


def my_index(l,x,default=False):
    if x in l:
        return l.index(x)
    else:
        return default

def judge(a,b):
    n = a+b
    ans = -1
    while(n>0):
        if n==1:
            ans = 0
            break
        elif n%2 == 1:
            ans = 1
            break
        elif n%2 == 0:
            n = n/2
    return ans


'''while(a_odds!=[]):
    for i in range(len(a_odds)):
        if judge(a_odds[0],a_odds[i])==0 and i!=0:
            count += 1
            a_odds.pop(i)
            break
    a_odds.pop(0)'''

while(a_odds!=[]):
    temp = a_odds[0]
    a_odds.pop(0)
    if a_odds ==[]:
        break
    for i in alist:
        b = i-temp
        if (i-temp) in a_odds:
            count += 1
            a_odds.pop(a_odds.index(i-temp))
            break
    
    
while(a_even!=[]):
    temp = a_even[0]
    a_even.pop(0)
    if a_even==[]:
        break
    for i in alist:
        if (i-temp) in a_even:
            count += 1
            a_even.pop(a_even.index(i-temp))
            break
    

print(count)

Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)

Buggy python submission (verdict: Runtime Error):
import math

N = int(input())
a = list(map(int,input().split()))
a_odds = []
a_even = []

for i in range(N):
    if a[i]%2 != 0:
        a_odds.append(a[i])
    else:
        a_even.append(a[i])

a_odds.sort()
a_odds.reverse()
a_even.sort()
a_even.reverse()

count = 0
alist = []
max= 0
if a_odds!=[] and a_even!=[]:
    max = max(a_odds[0],a_even[0])
elif a_odds ==[]:
    max= a_even[0]
elif a_even == []:
    max = a_odds[0]
    
for i in range(round(math.log2(max))+1,0,-1):
    alist.append(2**i)


def my_index(l,x,default=False):
    if x in l:
        return l.index(x)
    else:
        return default

def judge(a,b):
    n = a+b
    ans = -1
    while(n>0):
        if n==1:
            ans = 0
            break
        elif n%2 == 1:
            ans = 1
            break
        elif n%2 == 0:
            n = n/2
    return ans


'''while(a_odds!=[]):
    for i in range(len(a_odds)):
        if judge(a_odds[0],a_odds[i])==0 and i!=0:
            count += 1
            a_odds.pop(i)
            break
    a_odds.pop(0)'''

while(a_odds!=[]):
    temp = a_odds[0]
    a_odds.pop(0)
    if a_odds ==[]:
        break
    for i in alist:
        b = i-temp
        if (i-temp) in a_odds:
            count += 1
            a_odds.pop(a_odds.index(i-temp))
            break
    
    
while(a_even!=[]):
    temp = a_even[0]
    a_even.pop(0)
    if a_even==[]:
        break
    for i in alist:
        if (i-temp) in a_even:
            count += 1
            a_even.pop(a_even.index(i-temp))
            break
    

print(count)

Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)

Buggy python submission (verdict: Time Limit Exceeded):
N = int(input())
a = list(map(int,input().split()))
a_odds = []
a_even = []

for i in range(N):
    if a[i]%2 != 0:
        a_odds.append(a[i])
    else:
        a_even.append(a[i])

a_odds.sort()
a_odds.reverse()
a_even.sort()
a_even.reverse()

count = 0
def judge(a,b):
    n = a+b
    ans = -1
    while(n>0):
        if n==1:
            ans = 0
            break
        elif n%2 == 1:
            ans = 1
            break
        elif n%2 == 0:
            n = n/2
    return ans


while(a_odds!=[]):
    for i in range(len(a_odds)):
        if judge(a_odds[0],a_odds[i])==0 and i!=0:
            count += 1
            a_odds.pop(i)
            break
    a_odds.pop(0)

while(a_even!=[]):
    for i in range(len(a_even)):
        if judge(a_even[0],a_even[i])==0 and i!=0:
            count += 1
            a_even.pop(i)
            break
    a_even.pop(0)


print(count)

Fixed submission:
n = int(input())
a = list(map(int, input().split()))
a.sort()
b = {}
for i in range(len(a)):
    if a[i] in b:
        b[a[i]] += 1
    else:
        b[a[i]] = 1
twins = []
now = 1
while now <= a[-1]:
    now *= 2
    twins.append(now)
for i in range(len(a) - 1, -1, -1):
    tmpa = 0
    if  b[a[i]] == 0:
        continue
    for j in range(len(twins) - 1, -1, -1):
        if twins[j] <= a[i]:
            break
        tmpa = twins[j] - a[i]
    if tmpa == a[i]:
        if b[tmpa] >= 2:
            b[tmpa] -= 2
    elif tmpa in b and b[tmpa] != 0:
        b[tmpa] -= 1
        b[a[i]] -= 1
countb = 0
for i in b:
    countb += b[i]
print((n - countb) // 2)