Structural Mechanics

Let 22 2 ˆˆˆˆ ˆ ˆ() ( ) S I yz i zx j xy k x i y j z kd S    , where S denotes the surface of the sphere of unit radius centered at the origin. Here ˆˆˆ, a n d ij k denote three orthogonal unit vectors. The value of I is ____________