PPSWOR — probability at the third draw

Consider a population of size $N=6$ as $\{1,2,3,4,5,6\}$ with auxiliary values $x_1=100$, $x_2=200$, $x_3=300$, $x_4=400$, $x_5=500$, $x_6=500$. A sample of $n=3$ is drawn using PPSWOR, with $U_r$ the unit selected at the $r$th draw. Then $\mathbb{P}[U_3=2\mid U_1=5, U_2=3]=$