The formula to calculating it is:

So the code I made is this:

```
p=int(input('Tell me your weight.(kg)'))
x=int(input('Tell me your height.(cm)'))
e=(x/100)**2
r=p/e
if r<=25:
print('Your body mass index is',round(r),'and you are thin.')
elif r>=30:
print('Your body mass index is',round(r),'and you are fat.')
else:
print('Your body mass index is',round(r),'and you are normal.')
```

- First to know the person's mas weight and height we ask the using input
- Then I do the operations for height: pass the cm to m and square it
- Do the rest of the operations
- And depending on your number giving the result

An example of what the running code would look like:

Sources:

The source to all the mathematical values are in Wikipedia