9.8.4 Surface integrals

3) Problem: Calculate the surface integral of the \( 1^{\text {st }} \) kind: \[ \iint_{S} \sqrt{x^{2}+y^{2}} d S \] where \( S \) is the part of the conical surface \( z=\sqrt{x^{2}+y^{2}} \), distinguished by the condition \( z \leq 1 \).