Freestyle swimming - 1 km without stops

I really want to improve my swimming skills, because current level is not good. I'm interested in distance more than in speed. I don't have style limitations, but I think I will use only crawl and backstroke.

I'm going to achieve this goal till the end of the year. Actually I think it's possible to accomplish earlier, but I don't have strict time limits and currently I don't know how I will setup my trainings.

Currently I can swim about 100 meters by crawl without stops