KöMaL 2012 B4443

$a_1$,$a_2$,...,$a_n$ és $b_1$,$b_2$,...,$b_k$ are two given sequences with positive integer terms with $a_i \le k$ and $b_j \le n$. Show that there are integers 0$\le i_1$<$i_2 \le n$ and 0$\le j_1$<$j_2 \le k$ such that $a_{i_1+1}+\ldots +a_{i_2}=b_{j_1+1}+\dots +b_{j_2}$.