UCR: casting a string that is a result of split_string to int

I am developing a report on commcare , this is an issue that I have been struggling with alot.
This will return a string e.g “2011”
“expression”: {
“type”: “split_string”,
“string_expression”: {
“type”: “property_name”,
“property_name”: “dob_eth”
},
“index_expression”: {
“type”: “constant”,
“constant”: 0
},
“delimiter”: “-”
}

I wanted to cast this string(2011) to integer and increment it by 1.
I am using this on named expression or base item expression not configured indicators.
How Can I do that?