first redefine the function:
(n-1)+1 ...... when n-1 ≥ 0.........n ≥ 1
-(n-1)+1 .......when n-1 < 0..........n < 1
then solve it:
n-1+1 = n =0 ( doesn't belong to the interval)
-n+1+1 = -n + 2 = 0, n = 2 ( doesn't belong to the interval either)
no solution for n ∈ R
