AMC1301 voltage sensing

[m.jayid]

Hi everybody .
I would like to use the AMC1301 as a voltage sensor .to sense the input of a DC source =400V.
according to its datasheet the voltage drop between VINP and VINN should be maximum 250mV.
I choose R1=R2=1Mohm.
What would be the values of R3 and R3'.

Thank you .