Human: Can you show me a Python function to the greatest common divisor of three numbers. Assistant: 
Here is a Python function to the greatest common divisor of three numbers

import math

def gcd(a, b, c):
    """Returns the greatest common divisor of a, b, and c."""
    return (a * b * c) % (a * (b % c))

# Enter the numbers
a = 10
b = 15
c = 20

# Calling the function
print((gcd(a, b, c)))

#Example Output
# 0

#Remember to inspect code for bugs.