Petya loves lucky numbers. Everybody knows that positive integers are lucky if their decimal representation doesn't contain digits other than $4$ and $7$. For example, numbers $47, 744, 4$ are lucky and $5, 17, 467$ are not.

Lucky number is super lucky if it's decimal representation contains equal amount of digits $4$ and $7$. For example, numbers $47, 7744, 474477$ are super lucky and $4, 744, 467$ are not.

One day Petya came across a positive integer $n$. Help him to find the least super lucky number which is not less than $n$.

The only line contains a positive integer $n (1 \le n \le 10^9)$. This number doesn't have leading zeroes.

Output the least super lucky number that is more than or equal to $n$.