6. Executing the flowchart shown in the figure, the output value of $S$ is\\ (A) $- \frac { \sqrt { 3 } } { 2 }$\\ (B) $\frac { \sqrt { 3 } } { 2 }$\\ (C) $- \frac { 1 } { 2 }$\\ (D) $\frac { 1 } { 2 }$