S 1 2 r 2

S 1 2 r 2S 1 2 r 2S 1 2 r 2S 1 2 r 2S 1 2 r 2S 1 2 r 2
S 1 2 r 2S 1 2 r 2S 1 2 r 2S 1 2 r 2