Build a Python function for calculating the digital root of a positive integer.
A digital root is obtained by recursively summing all the digits of a number until a single digit number is left. For instance, the digital root of 54817 is 7, because summing 5+4+8+1+7 gives 25, which can be further reduced to 2+5, which sums to 7. For this task, your aim is to construct a function, `digital_root`, that takes a positive integer as a parameter and returns its digital root. ### Parameters - `n`: A positive integer. This is the number whose digital root needs to be found. ### Return Value - The function should return the digital root of `n`. ### Examples ```python # For 16, 1+6 equals 7, a single digit number. digital_root(16) # returns: 7 # For 456, 4+5+6 equals 15. Reducing 15 gives 1+5 equals 6, a single digit number. digital_root(456) # returns: 6 # For 54817, 5+4+8+1+7 equals 25. Reducing 25 gives 2+5 equals 7, a single digit number. digital_root(54817) # returns: 7 ```