Getting Error while trying to create a script field to add two number custom fields

[Yatam_ Annapurna]

Script:

import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.ComponentManager
import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.CustomFieldManager
import com.atlassian.jira.issue.fields.CustomField
import com.atlassian.plugin.osgi.container.OsgiContainerManager
import com.atlassian.jira.user.ApplicationUser

def A = getCustomFieldValue("Luck")
def B = getCustomFieldValue("Tempo Hours")

def C = A-B

Return C

...........

I am getting static type error at "-".

Could someone please help me on how to create the calculated field which can substarct A from B