1.
If x>0x > 0, y>0y > 0, z>0z > 0, xy+yz+zx<1xy + yz + zx < 1 and if tan1x+tan1y+tan1z=π\tan^{-1} x + \tan^{-1} y + \tan^{-1} z = \pi, then x+y+zx + y + z equals to