The solution of the differential equation

$\frac{dy}{dx}$ – y$^{2}$ = 0, given y=1 at x=0 is

1. $\frac{1}{1+x}$
2. $\frac{1}{1-x}$
3. $\frac{1}{(1-x)^2}$
4. $\frac{x^3}{3}$+1