Thank you so much man, I was struggling very hard here and you saved me.

OMG... I really need more than 2 hours to finish this one.

You can see the inputs just be printing them to the console ... .WriteLine(...) iirc in C#
for instance: "(C5H5)Fe(CO)2CH3"

You can check the formula yourself: https://github.com/codewars/codewars.com/wiki/Troubleshooting-your-solution#how-can-i-see-which-input-causes-my-solution-to-fail

You can check the edge cases yourself: https://github.com/codewars/codewars.com/wiki/Troubleshooting-your-solution#how-can-i-see-which-input-causes-my-solution-to-fail

I don't know which language you're trying but printing the input would help: https://github.com/codewars/codewars.com/wiki/Troubleshooting-your-solution#print-input
And you can check the expected results are ok in some page like: https://www.wolframalpha.com/

The input is a string of only digits

There are no points, so there are no floating-point numbers afaik