If all you plan on doing is play Minecraft, try that. Like the above poster said, I am not sure what you have, so I didn't include OS, kb/m, or monitor.
Using charmer's setup would give you very little room for upgrades, but it's hard to get something better for 300 euros... The OS alone costs 80 euros....
I changed the CPU to 370K because having a dedicated graphics card renders the iGPU in the A6-5400K useless. With the 370K, you'll get a marginally better CPU performance. I also downgraded the memory to 1600 MHz, because higher speeds show a performance improvement with A6-5400K but not with 370K. Upgrading to a Radeon 7770 will allow you to record ~60 FPS with medium settings on Minecraft, I would think.