Maija has discovered new matter! She has identified 26 new particles in total. Fortunately she has decided to spare herself and everyone else the effort and just named them with the lowercase Latin letters $a-z$. The particles often appear in string formations and interact with each other in mysterious ways that Maija intends to uncover. Currently she has found that all strings have a potential that is equal to the squares of the different particles' cardinalities. Formally, the potential of a string $s$ that contains $cnt_a$ $a$-particles, $cnt_b$ $b$-particles, $\dots$ and $cnt_z$ $z$-particles has a potential $pot_s = cnt_a^2 + cnt_b^2 + ... + cnt_z^2$. The strings are quite volatile: if their potential falls short of $W$, then they will immediately explode.

Maija is attempting to pick a sample from string $s$. Find the shortest possible sample she can cut from it.

Input

The first line contains a single integer $W$. The second line contains a string $s$.

Output

Print the shortest possible sample. If there are multiple answers, print any.

Constraints

• $1 \leq |s| \leq 10^5$
• $1 \leq W \leq 10^{10}$
• $W \leq pot_s$

Example 1

Input:

4
ccda

Output:

cc

Example 2

Input:

17
caacaabazz

Output:

aacaa