The value of (−5x2y)×(−23xy2z)×(815xyz2)×(−14z) is ______.
If |z1|=|z2|=|z3|=|z4|=1 and z1+z2+z3+z4=0 then least value of the expression E=|z1−z2|2+|z2−z3|2+|z3−z4|2+|z4−z1|2 is