Let $(X_n, \mathscr{F_n}), n \geq 0$ be a super martingale and $T$ an $\{F_n\}$-stopping time a.s. bounded by $N \lt \infty$. Show that
$$ E[|X_T|] \leq 3 \max_{n \leq N} E[|X_n|]$$
I can prove that $$ E[|X_T|] \leq E[\max_{n \leq N} |X_n|]$$. I am confused about how to get $3$ in the RHS.