I don't know if u see this puzzle before, but if u don't I BEG u not to get frustrated easily and then fire ur engine (though it will not find the solution quickly !) u will miss the beautiful moment in case u figured it out, for me I remember spending multiple sessions before I figured it out (as I took a vow NEVER to see a solutoin for a puzzle , u can imagine the number of waiting to be solved ones on my chess folder ! ) and believe me it was really an amazing moment .so think about it and in case u couldn't manage to figure out the key of the solution, save the position an a paper or ur phone and look it back again and again until u solve it :))
http://en.lichess.org/r91bawSU
http://en.lichess.org/r91bawSU