CF702B.Powers of Two

普及/提高-

通过率：0%

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题目描述

You are given $n$ integers $a_{1},a_{2},...,a_{n}$ . Find the number of pairs of indexes $i,j$ ( i<j ) that $a_{i}+a_{j}$ is a power of $2$ (i. e. some integer $x$ exists so that $a_{i}+a_{j}=2^{x}$ ).

输入格式

The first line contains the single positive integer $n$ ( $1<=n<=10^{5}$ ) — the number of integers.

The second line contains $n$ positive integers $a_{1},a_{2},...,a_{n}$ ( $1<=a_{i}<=10^{9}$ ).

输出格式

Print the number of pairs of indexes $i,j$ ( i<j ) that $a_{i}+a_{j}$ is a power of $2$ .

输入输出样例

输入#1
```
4
7 3 2 1
```
输出#1
```
2
```
输入#2
```
3
1 1 1
```
输出#2
```
3
```

说明/提示

In the first example the following pairs of indexes include in answer: $(1,4)$ and $(2,4)$ .

In the second example all pairs of indexes $(i,j)$ (where i<j ) include in answer.

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