The task is to take in a credit card number, and find out if it is a valid credit card number or

not. Credit card numbers follow an algorithm called "Luhn's algorithm".

The formula verifies a number against its check digit, which is the last digit. This number

must pass the following test:

From the rightmost digit, which is the check digit, and moving left, double the value of every

second digit. If the result of this doubling operation is greater than $9($e$.$g$.,8\backslash$times $2=16),$ then

add the digits of the product $($e$.$g$.,16$: $1+6=7,18$: $1+8=9)$ or$,$ alternatively, the same

result can be found by subtracting $9$ from the product $($e$.$g$.,16$: $16-9=7,18$: $18-9=9).$

Take the sum of all the digits.

If the total modulo $10$ is equal to $0($if the total ends in zero$)$ then the number is valid

according to the Luhn formula; else it is not valid.

Assume an example of an account number $"7992739871"$ that will have a check digit added,

making it of the form $7992739871$x$.$ The sum of all the digits, processed as per steps $1$ and $2,$

is $67+$x$.$ Thus x must be $3$ to bring the total to be modulo $10=0.$ If x is not $3,$ then this is not

a valid credit card number.

Input Format

An n$-$digit credit card number, where the last digit is the check digit.

Output Format

Output "VALID" if it is a valid credit card number and "INVALID" if it is not.

Constraints

$4<=$n$<=30$

Sample Input

$4539682995824395$

Sample Output

VALID

Explanation

Make sure to read from right to left.

Every second digit from the last digit.

$4539682995824395$

$5+3+2+5+9+8+9+5=46$

Double every second digit from the second last digit and subtract $9$ if needed.

$4539682995824395$

$2*9=18$; $18-9=9$

$2*4=8$

$2*8=16$; $16-9=7$

$2*9=18$; $18-9=9$

$2*2=4$

$2*6=12$; $12-9=3$

$2*3=6$

$2*4=8$

$9+8+7+9+4+3+6+8=54$

Adding these together

$46+54=100$

$100\%10==0$ So the card is VALID