how can i resolve minus value o/p

how can i resolve minus value o/p

hi
good aftn.

if we give minus values from 0 to -11  then the output should be as minus value i.e -11.if we give greater than -11 that is -12,-13 likewise then the output should be the given respective minus value.Have to resolve this using change event.   
for ex: if textbox1=-8 then the output should be -11.
if textbox1=-20 then the o/p should be -20.
please anyone help me....