Given an array arr[] of size N, find the first digit from the left of the product of these N integers.

Example 1:

Input: N = 4, arr[] = {5, 8, 3, 7}
Output: 8
Explanation: Produt is 840

Example 2:

Input: N = 3, arr[] = {6, 7, 9} 
Output: 3
Explanation: Produt is 378

Your Task:
You don't need to read input or print anything. Your task is to complete the function firstDigit() which takes N and array arr[] as input parameters and returns the left digit of product.

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

Constraints:
1 ≤ N, arr[i] ≤ 10⁵