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Basic Accuracy: 56.71% Submissions: 240 Points: 1

Given a non-negative integer N, repeatedly add all its digits until the result has only one digit.

Example 1:

Input:
N = 98

Output:
8

Explanation:
Sum of digit of N = 98  is 9 + 8 = 17
Sum of digit of 17 = 1 + 7 = 8
Since 8 is the single digit number hence it is the
required answer.

Example 2:

Input:
N = 1

Output:
1

Explanation:
Since 1 is the single-digit number hence it is the
required answer.

You don't need to read input or print anything. Your task is to complete the function singleDigit() which takes an integer N as an input parameter and return the single-digit you will get after repeatedly adding the digits of N.

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

Constraints:
1 <= N <= 1018