```
numOfYears = 0
cpi = eval(input("Enter the CPI for July 2015: "))
if cpi.isdigit():
    while cpi < (cpi * 2):
        cpi *= 1.025
        numOfYears += 1
    print("Consumer prices will double in " + str(numOfYears) + " years.")
while not cpi.isdigit():
    print("Bad input")
    cpi = input("Enter the CPI for July 2015: ")

```

I'm getting the following error.

> 
> AttributeError: 'int' object has no attribute 'isdigit'
> 
> 
> 

Since I'm new to programming, I don't really know what it's trying to tell me. I'm using the `if cpi.isdigit():` to check to see if what the user entered is a valid number.