How to raise more than one exception in python

I try to raise more than one exception in an if-else branch: The code is the following:

x = input()
try:
    if int(x) < 0: # the number should not be a negative number
        raise("This is a negative number.")
    if int(x) >= 4:
        print("That a lot.")
    else:
        print("That is not so much.")
except ValueError: # the input should be a other than a number
    print("You did not entered a number.")

The following error message occurs: TypeError: exceptions must derive from BaseException