solving a 3D systems of equations

I am trying to solve the following systems of equations for x, y and z:

{
xyz=a
x+y+z=w
}

x<y<z (i.e., x is not equal to y or z & y is not equal to z)
'a' and 'w' are given quanitites.

How can I solve the system?

Thanks in advance

.