在$△ABC$中，点$M$，$N$满足$\stackrel{\rightharpoonup }{AM}=2\stackrel{\rightharpoonup }{MC}$,$\stackrel{\rightharpoonup }{BN}=\stackrel{\rightharpoonup }{NC}$．若$\stackrel{\rightharpoonup }{MN}=x\stackrel{\rightharpoonup }{AB}+y\stackrel{\rightharpoonup }{AC}$，则$x=$；$y=$．