Can anyone answer why my code is not working

https://www.codechef.com/viewsolution/39955968
my code is not working.I couldn’t figure out what is my problem.Can somebody help me out?

Your code won’t work for test cases like 3 0 0 0 0 0 5 because the fuel will be over when you come till 4th car. So, the answer will be 3 only and not 8. Hope you got my logic.