Takahashi has N balls with positive integers written on them. The integer written on the i-th ball is A_i. He would like to form some number of pairs such that the sum of the integers written on each pair of balls is a power of 2. Note that a ball cannot belong to multiple pairs. Find the maximum possible number of pairs that can be formed.

Here, a positive integer is said to be a power of 2 when it can be written as 2^t using some non-negative integer t.

Constraints

* 1 \leq N \leq 2\times 10^5
* 1 \leq A_i \leq 10^9
* A_i is an integer.

Input

Input is given from Standard Input in the following format:


N
A_1 A_2 ... A_N


Output

Print the maximum possible number of pairs such that the sum of the integers written on each pair of balls is a power of 2.

Examples

Input

3
1 2 3


Output

1


Input

5
3 11 14 5 13


Output

2
N = int(input())
A = [int(a) for a in input().split()]

dic = {}
for a in A:
    if a in dic:
        dic[a] += 1
    else:
        dic[a] = 1
        
A.sort(reverse=True)
ans = 0
for a in A:
    if dic[a] == 0:
        continue
    dic[a] -= 1
    num = pow(2, len(bin(a))-2) - a
    if num in dic and dic[num] > 0:
        ans += 1
        dic[num] -= 1

print(ans)