Given two irreducible fractions defining an interval, we investigate the problem of finding the fraction of smallest
denominator in this interval. Keeping integers as small as possible can be crucial for exact arithmetic computations. Indeed,
even if exact arithmetic libraries [3] provide efficient tools to handle exact computations on arbitrarily large integers, dealing
with big integers remains computationally expensive. Thus, when a parameter value has to be chosen in a given interval,
it may be interesting to choose the value involving integers as small as possible to enable fast computations. This problem
also has a nice geometric interpretation and arises for instance in the computation of the integer hull of a polygon [5].
In this note, we consider two irreducible proper fractions f and g such that 0 ≤ f < g ≤ 1. We give a characterization of
the irreducible proper fraction h such that f < h < g and the denominator of h is as small as possible. Finally, we provide
an output-sensitive algorithm to compute h from the continued fraction decompositions of f and g.