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
import os
import sys
from collections import Counter

if os.getenv("LOCAL"):
    sys.stdin = open("_in.txt", "r")

sys.setrecursionlimit(2147483647)
INF = float("inf")
IINF = 10 ** 18
MOD = 10 ** 9 + 7

N = int(sys.stdin.readline())
A = list(map(int, sys.stdin.readline().split()))

# グラフの最大マッチングだと辺の数多すぎ
# 大きい数から見ていくとまだ見てない数のうちペアになれる数が1つに定まる

A.sort(reverse=True)
counts = Counter(A)
ans = 0
for a in A:
    if counts[a] <= 0:
        continue
    counts[a] -= 1
    b = (1 << a.bit_length()) - a
    if counts[b] > 0:
        ans += 1
        counts[b] -= 1
print(ans)
