next(1,2).
next(2,3).
next(3,4).
next(4,5).
next(5,6).
next(6,7).
next(7,8).
next(8,9).
next(9,10).
next(10,11).
next(11,12).
next(12,13).
next(13,14).
next(14,15).
next(15,16).
next(16,17).
next(14,18).
next(18,19).
next(19,20).
next(20,21).
next(18,22).
next(22,23).
next(23,24).
next(24,25).
next(22,26).
next(26,27).
next(27,28).
next(28,29).
next(29,30).
next(30,31).
next(28,32).
next(32,33).
next(33,34).
next(34,35).
next(32,36).
next(36,37).
next(37,38).
next(38,39).
next(39,40).
doAt(startflow,3).
doAt(a20,5).
doAt(a19,6).
doAt(a5,7).
doAt(a25,8).
doAt(a13,9).
doAt(a24,10).
doAt(a7,11).
doAt(a10,12).
doAt(a6,13).
doAt(a17,14).
doAt(a23,15).
doAt(endflow,16).
doAt(a4,18).
doAt(a3,19).
doAt(endflow,20).
doAt(a11,22).
doAt(a21,23).
doAt(endflow,24).
doAt(a12,26).
doAt(a14,27).
doAt(a8,28).
doAt(a18,29).
doAt(endflow,30).
doAt(a2,32).
doAt(a16,33).
doAt(endflow,34).
doAt(a1,36).
doAt(a15,37).
doAt(a22,38).
doAt(endflow,39).
subsAt(a20,4).
leftrightnexts(33,36).
leftrightnexts(29,32).
leftrightnexts(23,26).
leftrightnexts(19,22).
leftrightnexts(15,18).