Types of Vectors

Unit vector in the direction of sum of vectors $\overrightarrow{a}=2\hat{i}-\hat{j}+\hat{k}$ and $\overrightarrow{b}=2\hat{j}+\hat{k}$ is $\pm \frac{x\hat{i}+y\hat{j}+z\hat{k}}{m}$. Find $x+y+z+m$.