I am new to pine script and I am trying to get nifty 50 index ATM strike price automatically from current market price using the below code.
spot_atm_NF = input.int((50*math.round(spot_close/50)), title = "Ref -Strike" ,group=grpNifty,inline="NF")

But I am getting this error:

Cannot call 'input.int' with argument 'defval'='call 'operator *' (series int)'. An argument of 'series int' type was used but a 'const int' is expected.

Can somebody help me resolving this issue? Thanks.