Sum of Dataframe Column and use it on Ifelse condition

import pandas as pd 
  
# initialize data of lists. 
data = {'Name':['Tom', 'nick', 'krish', 'jack'], 'Age':[20, 21, 19, 18]} 
  
# Create DataFrame 
df = pd.DataFrame(data) 
  
# Print the output. 
df

a = df['Age'].sum()
b = 50
if b > a:
    print("b is greater than a")
elif a == b:
    print("a and b are equal")

I got the following error in python

"ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all()."

How can I print the if-else condition?