Gabriel is playing 2048. In this game, squares appear with a number on it. All the numbers are positive powers of $2$. You can combine two of the same power to get one power greater. For example, if you combine two $32$s you get a $64$ square. Gabriel has $N$ squares and wants to know the biggest square he can obtain from combining.

Input Specification

A single integer, $N$ $(1\le N\le 1000)$, the number of squares.

The second line contains $N$ integers, $x_i$, the number on the squares. $x_i=2^p,p\in [1,20]$

Output Specification

A single integer, the biggest square can Gabriel can theoretically create.

Sample Input 1

3
2 4 2

Sample Output 1

8

Explanation for Sample Output 1

Gabriel can combine the two $2$s to make a $4$ and then he can combine the two $4$s he has to make an $8$.

Sample Input 2

5
2 2 8 16 32

Sample Output 2

32

Explanation for Sample Output 2

Although Gabriel can combine the two $2$s, he cannot make any more moves. The biggest square he has is $32$.