Loop and trace

1

i have an object called input_obj i want to trace a property value in it.

 trace(input_obj.item[0].catagory[0].product[0].size1);
trace(input_obj.item[0].catagory[0].product[0].size2);
trace(input_obj.item[0].catagory[0].product[0].size3); 
this works but i need to loop through and trace.

this wont work


     for(i=1;i<6;i++){
    trace(input_obj.item[0].catagory[0].product[0].size+i);
}

Returns NaN