s 3
t 3
( s 1 , s 2 )
(2, 0)
(6, 5)
( t 1 , s 2 )
(7, 2)
(10, 2)
( s 1 , t 2 )
(3, 3)
(1, 2)
( t 1 , t 2 )
(12, 2)
(5, 3)