10           20
         [S1]----(R1)-------------(R4)
                  |                |
                  |                |
                  |10              |10
              10  |                |
         [S2]----(R2)-------------(R3)----[R]
                  |        10      |   10
                  |                |
                  |10              |10
              10  |                |
         [S3]----(R5)-----(R6)----(R7)
                      100      10