How to fix invalid literal for int() with base 10: '' : new to python. Using python3.7 and tkinter to make a GUI, where I grab the input from 2 text boxes, and use a math formula then export it out.

I've looked through other forms and tried what they suggested and could not find how to fix it. I've tried global inside and outside of the function, setting the variable before the function.

```python
def retrieve_input():
    global InputValue
    global InputValue2
    global Delay
    InputValue=tasks.get()
    InputValue2=proxies.get()
    print(InputValue)
    print(InputValue2)
    Delay=3500/int(InputValue)*int(InputValue2)
    print(Delay)
retrieve_input()
Label (window, width=12, text=Delay,bg="white",fg="Pink", font="none 22 bold") .grid(row=5, column=0,sticky=W)
```

  File ", line 29, in retrieve_input
    Delay=3500/int(InputValue)*int(InputValue2)
ValueError: invalid literal for int() with base 10: ''

Thank you :)