$\text { What is the minimum vertical distance between the parabolas } y = x ^ { 2 } + 4 \text { and } y = x - x ^ { 2 } \text { ? }$

$\text { What is the minimum vertical distance between the parabolas } y = x ^ { 2 } + 4 \text { and } y = x - x ^ { 2 } \text { ? }$