しかない
Usage
Used to express the fact that there is no other way, and that this is the only thing one can do
Examples
ここまで頑張ったんだから、最後までやるしかない
You've worked hard to come all this way, so you don't have any choice but to follow it through the end
チケットを持ってくるのを忘れたので、入り口でまた買うしなかった
I had forgotten to bring my ticket along, so I had no choice but to buy another one at at the entrance