Stoppa inläsning av värden i do-loop när man skriver en bokstav?

Uppgift: Given a list L of numbers, the span of L is defined as the highest minus the lowest value in L.
For instance, if L = [2, 15, 2, 10, 1, 9, 3]then the span of Lis 14( = 15 – 1).
Write a program that reads a list of integer values and then displays the list span. The program
should start by requesting to the user the values of list L. The user indicates the end of the list by
typing a non-numeric value (e.g. ctrl-z or a character like 'x') and only integers are entered,
otherwise.

Running example 1
Enter list: 2 15 2 10 1 9 3 x
List span = 14

Running example 2
Enter list: 2 2 2 2 x
List span = 0

Running example 3	
Enter list: 3 4 87 -15 20 x
List span = 102