Selecting ATM option of next month expiry

hey there ,
Need help regarding selection of strike for “next month” expiry with 40+ days to go.

in the option chain , you can see , ATM strike is at 20150 .
But , i need to create a straddle at equal premium/or equal delta of 0.5 which is one strike above at 20200.
Need help for keyword as tried “round” keyword , doesn’t seem to work.