Problem Description

Takahashi remembers paying \( N \) yen for an apple pie at the ABC patisserie.

This store charges an 8 percent consumption tax on food items. That is, when buying an apple pie with an untaxed price of \( X \) yen, you must pay \( X \times 1.08 \) yen (rounded down to the nearest integer).

Takahashi has forgotten the untaxed price \( X \) of the apple pie and wants to know it. Write a program that takes \( N \) as input and finds \( X \). Note that \( X \) should be an integer.

If there are multiple possible untaxed prices, output any one of them. Also, there is a possibility that Takahashi misremembered the amount paid \( N \), so if no possible untaxed price for the apple pie exists, report that.

Input Format

The input is given from the standard input in the following format:

\( N \)

Output Format

If a possible untaxed price \( X \) exists, output one such integer \( X \).
If multiple such values exist, you may output any one of them.
If no possible untaxed price exists, output :(.

Sample Input and Output

Sample Input #1

432

Sample Output #1

400

Sample Input #2

1079

Sample Output #2

:(

Sample Input #3

1001

Sample Output #3

927

Notes/Hints

Constraints

• \( 1 \leq N \leq 50000 \)
• \( N \) is an integer

Sample Explanation 1

When the untaxed price of the apple pie is 400 yen, the amount to be paid is \( 400 \times 1.08 = 432 \) yen. For any other untaxed price, the amount to be paid would not be 432 yen.

Sample Explanation 2

There is no untaxed price that results in a payment of 1079 yen.

Sample Explanation 3

When the untaxed price of the apple pie is 927 yen, the amount to be paid is \( 927 \times 1.08 = 1001.16 \), which rounds down to 1001 yen.

见题面 Input 部分

见题面 Output 部分