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Number of 1's in smallest repunits
Easy Accuracy: 36.34% Submissions: 223 Points: 2

Every number whose unit’s digit is 3 has a repunit as its multiple. A repunit is a number which has only ones. It is of the form (10n – 1)/9. Example: 3 divides 111, 13 divides 111111.
A positive integer N will be given whose unit’s digit is 3. The task is to find the number of 1s in the smallest repunit which is divisible by the given number N.

Example 1:

Input: N = 3
Output: 3
Explaination: The number 111 is the first
repunit which is divisible by 3.

Example 2:

Input: N = 13
Output: 6
Explaination: The first repunit is 111111
which divisible by 13.

You do not need to read input or print anything. Your task is to complete the function repUnit() which takes N as input parameter and returns the number of 1 in the smallest repunit which is divisible by N.

Expected Time Complexity: O(N)
Expected Auxiliary Space: O(1)

Constraints:
1 ≤ N ≤ 106