If f(x) = x + 1; and g[f(x)] = x; what is g(x)?

PLEASE HELP!

"If f(x) = x + 1; and g[f(x)] = x; what is g(x)? "

if f(x) = x+1
and g(f(x)) = g(x+1) =x ....(1)

What rule would convert (x+1) to x for all values of (x+1)?

Note: In this particular case, where f(g(x))=x, we call g(x) the inverse of f(x).