ErdosErdős, Ginzburg and Ziv prove the following: Let $n \geq 1$¸ and $a_1,\ldots, a_{2n-1}\in \mathbb{Z}$. There exist distinct $i_1,\ldots , i_n$ such that: $$a_{i_1} + \cdots + a_{i_n} \equiv 0 \pmod{n}$$$$ a_{i_1} + \cdots + a_{i_n} \equiv 0 \pmod{n}. $$ Is there a proof that doesn't use Chevalley-Warningthe Chevalley–Warning theorem (or a variant of its proof)?