Reaction between photon and proton

[programmer1115]

A high energy proton can collide with a photon to produce a charged pion and a neutron. If the photon comes from the cosmic microwave background and has an energy equivalent to a temperature of 3 K, what is the minimum energy of the proton in eV necessary to allow this reaction?

I'm thinking about momentum of a photon and stuff.. is my approach correct ? if not what should be done ?

 

[csopi]

So the reaction is:
$$p^+ + ph \rightarrow pion + n^0$$

The energy of the left handside must not be less, than that of the right handside, so you'll just have to look up the energies of the neutron and pion (zero velocity).