Please read this: https://github.com/codewars/codewars.com/wiki/Troubleshooting-your-solution . Also if you want someone to help you out you should post your code here and mark it as having spoiler content.

Finally it worked! Thanks.

This seems to not be the case.
Still errors on "random silly tests"

yes

I think so, for one second I thought, that expected and submitted are swapped, but both expected and submitted numbers are wrong. Should I post a code?

I guess that C "random silly tests" is still rough.
x = 276492

y = 477479

Expected: 1846414315

My C-programm passes 18 out of 19 tests (last test failed). Can't figure out where the problem is...