help on strategy for a game????

the game is as follows: 

                 Agent 2

                C       D
             ________________
            |       |       |
          C | 3, 3  |  1, 5 |
            |_______|_______|
Agent 1     |       |       |
          D | 5, 1  |  0, 0 |
            | ______|_______|


The game is to be played 1000 times against another agent... No fixed
strategy seems to work against all other fixed stategies... suggest
some cooperative mixed strategy for this game please.