Running. Training for a half marathon!!
Do you have any troubles with your knees or do you have pain after runnunig? If not, everything is fine. Just go to a store and buy a good pair of shoes. They will advise you.
If possible, buy to different pair of shoes. You will need more shoes if you run frequently and it's good to change them, cause every shoe is little different and it's better for your feet and legs.