If $\vec a,\vec b,\vec c$ are $3$ vectors such that
\[
\vec b=2\hat i-\hat j,\qquad \vec c=\hat j+2\hat k,
\]
\[
|\vec a+\vec b|=3,\qquad |\vec a\times(\vec b\times\vec c)|=3\sqrt2
\]
and
\[
(\vec a,\vec b\times\vec c)=\frac{\pi}{3},
\]
then $\vec a\cdot\vec b=$