\documentclass[11pt]{scrartcl}
\usepackage{evan}
\begin{document}
\title{Shortlist 2013 C4}
\subtitle{Evan Chen}
\author{Twitch Solves ISL}
\date{Episode 77}
\maketitle
\section*{Problem}
Let $n$ be a positive integer, and let $A$ be a subset of $\{ 1,\dots ,n\}$.
An $A$-partition of $n$ into $k$ parts is a representation of $n$
as a sum $n = a_1 + \dotsb + a_k$,
where the parts $a_1$, \dots, $a_k$ belong to $A$ and are not necessarily distinct.
The number of different parts in such a partition is the number of
(distinct) elements in the set $\{ a_1 , a_2 , \dots , a_k \}$.
We say that an $A$-partition of $n$ into $k$ parts is optimal
if there is no $A$-partition of $n$ into $r$ parts with $r