Let $U$  be the universal set for sets $A$  and $B$ . If $n\left(A\right)=200,n\left(B\right)=300$  and $n\left(A\cap B\right)=100$  then $n\left(A^{|}\cap B^{|}\right)$  is equal to 300, then $n\left(U\right)$  is equal to