Help creating this equation and calculate once hit submit

im trying to build a queuing model using the previous picture as a code, im not an expert but is there a way to make it as a function where if a negative value is returned write error/or dont run? and how can i connect it to a button to calculate as it calculating automatically after every input.

this is what i have so far any help would be appreciated thank you

first, you can directly paste python code into a post instead of a screenshot if you use the markdown convention of putting it between 3 backticks. If you dont to run the script on every change of one of the inputs, use the st.form() method:

import streamlit as st

with st.form(key='form1'):
    a = st.number_input('a',value=1.)
    b = st.number_input('b',value=2.)    
    st.form_submit_button('press to calculate')

result = a + b**2
if result < 0 :
    st.error('negative result')
else:
    st.write(f'result is {result}')

thank you for the help @ksxx it worked and sorry about the screenshot learned my lesson for next time