Let $\mathrm{A}=\{1,3,4,6,9\}$ and $\mathrm{B}=\{2,4,5,8,10\}$. Let $\mathrm{R}$ be a relation defined on $\mathrm{A} \times \mathrm{B}$ such that $\mathrm{R}=\left\{\left(\left(a_{1}, b_{1}\right),\left(a_{2}, b_{2}\right)\right): a_{1} \leq b_{2}\right.$ and $\left.b_{1} \leq a_{2}\right\}$. Then the number of elements in the set R is :