Vector Algebra

Let \(a, b\) and \(c\) be unit vectors such that \(a\) is perpendicular to the plane containing \(\mathbf{b}\) and \(\mathbf{c}\) and angle between \(\mathbf{b}\) and \(\mathbf{c}\) is \(\frac{\pi}{3}\). Then, \(|\mathbf{a}+\mathbf{b}+\mathbf{c}|=\)