Consider the polytope
$P=\{(x_1,x_2,...,x_n)\in \mathbb{R}^n| \sum_{i=1}^n x_i=1; 0\leq a_i\leq x_i\leq b_i, i=1,...,n\}$
where $a_i$ and $b_i$ are constant lower and upper bounds for $x_i$. Is it true that the number of extreme points of $P$ is $O(n)$?