Use your calculator, summing up what you can. You can also try manually doing it:
$$ \frac{1}{1+\frac{1}{1+\frac{1}{1+\frac{1}{3}}}} $$
$$ =\frac{1}{1+\frac{1}{1+\frac{1}{\frac{4}{3}}}} $$
$$ =\frac{1}{1+\frac{1}{1+\frac{3}{4}}} $$
$$ =\frac{1}{1+\frac{1}{\frac{7}{4}}} $$
$$ =\frac{1}{1+\frac{4}{7}} $$
$$ =\frac{1}{\frac{11}{7}} $$
$$ = \boxed{\frac{7}{11}} $$