Let  $A=\{0,3,4,6,7,8,9,10\}$  and R be the relation defined on A such that  $R=\{(x,y)\in A\times A:x-y$  is odd positive integer or $x-y=2\}$ . The minimum number of elements that must be added to the relation R, so that it is a symmetric relation, is equal to ___.