jmc

There are two ways for a student to get $11$: $5+5+1$ and $5+3+3$. Clearly if someone gets one of these combinations someone else could get the other, so we are not guaranteed the most points with $11$. There is only one way to get $13$ points: $5+5+3$. In this case, the largest score another person could get is $5+3+3=11$, so having $13$ points guarantees having more points than any other person $\to \boxed{13}$.