import sys
values = (10, 20, 30, 40, 50)

#pos = input("Get the value at which position? ")
#pos = int(pos)

try:
    pos = int(input("Get the value at which position? "))
except ValueError:
    print("Position must be an integer.")
    sys.exit()

#if the position is invalid, ask until it is valid
while pos < 0 or pos >= 5:
#while pos >= 5 or pos < 0:
    print("Position must be between 0 and 4 inclusive.")
    pos = int(input("Get the value at which position? "))


if pos < 5 and pos >= 0:
    value = values[pos]
    print("The value at that position is", value)