[1,2,-1,1,4,-3,1,6,-5,1,8,-7,1,10,-9,1,12,-11,1, 14,-13,1,16,-15,1,18,-17,1,20,-19,1,22,-21,1,24, -23,1,26,-25,1,28,-27,1,30,-29,1,32,-31,1,34,-33, 1,36,-35,1,38,-37,1,40,-39]