Level 1 integral

$\begin{aligned} I & = \int_0^\pi (\sin x + \cos x)^2 \ dx \\ & = \int_0^\pi \left(\sin^2 x + 2\sin x \cos x + \cos^2 x \right) \ dx \\ & = \int_0^\pi \left(1 + 2\sin (2x) \right) \ dx \\ & = x - \frac {\cos (2x)}2 \ \bigg|_0^\pi \\ & = \pi \approx \boxed{3.142} \end{aligned}$