Gasoline

There are $N$ cars (numbered $1$ through $N$) on a circular track with length $N$. For each $i$ ($2 \le i \le N$), the $i$-th of them is at a distance $i-1$ clockwise from car $1$, i.e. car $1$ needs to travel a distance $i-1$ clockwise to reach car $i$. For each valid $i$, you can fill the $i$-th car's tank with up to $f_i$ litres of gasoline, with cost $c_i$ coins per litre. After that, yo