Unlocking car stereo

Question

My car battery went dead as an earth wire came undone and since then my stereo is asking for a 4 digit code.My car is a peugeot 306 and finding the code is really difficult compared to other cars and I really dont want to pay a specialist as its quite expensive.I have tried the decoders on the internet but I cant find one for peugeot.The seriel no. is PU-2294AC and Seriel no. is CL040120514536,can anyone help?