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
# B
import math

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

A_dict = dict()
for a in A_list:
    if a in A_dict.keys():
        A_dict[a] += 1
    else:
        A_dict[a] = 1

res = 0
A_list_ = list(reversed(sorted(A_list)))
for a in A_list_:
    # partner
    r = 2**math.ceil(math.log2(a))
    if a == r:
        res += A_dict[a] // 2
        A_dict[a] = 0
    else:
        b = r - a
        if A_dict[a] > 0 and A_dict.get(b, 0) > 0:
            A_dict[a] -= 1
            A_dict[b] -= 1
            res += 1
print(res)