Sure, it works...
verifican = 0
For registros_selected = 0 to Count()-1
MoveTo(registros_selected)
If IS_SELECTED = "1" Or IS_SELECTED = 1 Then verifican = verifican + 1
Next
NUM_REG_SELECTED = Mid(verifican,0,StrIn(verifican,"."))
or
NUM_REG_SELECTED = ToString(IS_SELECTED..SysTotalItems(M4_TOTAL_SUM), 0)