Also, for triggering new text/message entities every time a can is placed, it's handy to use a logic_case. Simply give your math_counter the following output:
OutValue "name of your logic_case" InValue 0.00
It will then send its value evertime it is changed. You need to specify those values in the logic_case entity as Cases (for example, put "1" as value for the Case01 keyvalue etc.)
Then you can work with the OnCaseXX Outputs of the logic_case to trigger the desired event at each possible amount of cans placed. For example, you could change the message of a game_text and Display it:
OnCase01 game_text AddOutput "message 2 cans left to retrieve" 0.00
OnCase01 game_text Display 0.01
OnCase02 game_text AddOutput "message 1 can left to retrieve" 0.00
OnCase02 game_text Display 0.01
etc pp