Let f_{1}(x)=\sqrt{1-x}, and for integers n \geq 2, let f_{n}(x)=f_{n-1}\left(\sqrt{n^{2}-x}\right). If N is the largest value of n for which the domain of f_{n} is nonempty, the domain of f_{N} is \{c\}. What is N+c ?
Answer Choices
A. -226
B. -144
C. -20
D. 20
E. 144