Concept:
Region is intersection of:
\[
x^2 + y^2 \le 1 \quad (\text{circle})
\]
\[
y^2 \le 1 - x \quad (\text{parabola})
\]
Step 1: Find limits.
Intersection gives:
\[
x^2 + (1-x) = 1 \Rightarrow x(x-1)=0 \Rightarrow x=0,1
\]
Step 2: Area expression.
\[
\text{Area} = \int_0^1 2\sqrt{1-x}\,dx + \int_{-1}^0 2\sqrt{1-x^2}\,dx
\]
Step 3: Evaluate.
\[
\int_0^1 2\sqrt{1-x}\,dx = \frac{4}{3}
\]
\[
\int_{-1}^0 2\sqrt{1-x^2}\,dx = \frac{\pi}{2}
\]
Step 4: Total area.
\[
= \frac{\pi}{2} + \frac{2}{3}
\]