PI = 3.14159
E = 2.71828

def add_numbers(a, b):
    return a + b

def concat_strings(str1, str2):
    return str1 + str2

# Test cases
if __name__ == "__main__":
    result1 = add_numbers(3, 5)
    print(f"add_numbers(3, 5) = {result1}")  # Expected output: 8