Let \( \mathbf{a} \), \( \mathbf{b} \), and \( \mathbf{c} \) be vectors of magnitude 2, 3, and 4 respectively. If:
- \( \mathbf{a} \) is perpendicular to \( (\mathbf{b} + \mathbf{c}) \),
- \( \mathbf{b} \) is perpendicular to \( (\mathbf{c} + \mathbf{a}) \),
- \( \mathbf{c} \) is perpendicular to \( (\mathbf{a} + \mathbf{b}) \),
then the magnitude of \( \mathbf{a} + \mathbf{b} + \mathbf{c} \) is equal to: