# decompose into a direct sum of irreps

I have got some problems such as:"Decompose the real representation $A$ of the group $G$ into a direct sum of irreps". Following problem is one of them.

Let $\Phi$ be the real representation of the cyclic group $C_4,$ such as $\Phi(c)=\begin{bmatrix}0 & 0 &-1\\0 & 1 & 0 \\1 & 0 & 0\end{bmatrix}.$

Decompose $\Phi$ into a direct sum of irreps.