Given a number, N. Find the sum of all the digits of N

Example 1:
Input:
N = 12
Output:
3
Explanation:
Sum of 12's digits:
1 + 2 = 3
Example 2:
Input:
N = 23
Output
5
Explanation:
Sum of 23's digits:
2 + 3 = 5
Your Task:
You don't need to read input or print anything. Your task is to complete the function sumOfDigits() which takes an integer N as input parameters and returns an integer, total sum of digits of N.
Expected Time Complexity: O(log_{10}N)
Expected Space Complexity: O(1)

Constraints:
1<=N<=10^{5}

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