imc

Since the side of the square is the diameter of the semicircle, the radius of the semicircle is $\frac{1}{2}\cdot \frac{2}{\pi }=\frac{1}{\pi }$. Since the length of one of the semicircular arcs is half the circumference of the corresponding circle, the length of one arc is $\frac{1}{2}\cdot 2\cdot \pi \cdot \frac{1}{\pi }=1$. Since the desired perimeter is made up of four of these arcs, the perimeter is $4\cdot 1=\boxed{4}$.