Problem Statement

Mr. Takahashi is marking examination papers of his students. Unfortunately, he has forgotten the correct answer to a certain question.

$N$ students answered this question by an integer between $0$ and $M$, inclusive. He has decided to assume the correct answer to be the integer $X$ if more than half of the students answered $X$.

You are given the answers of the $N$ students to this question. If he is going to assume the correct answer to be some integer $X$, print the value of $X$. If he is unable to assume the correct answer to be any integer, print ?.

Input

Input is given from Standard Input in the following format:

$N$ $M$ $A_1$ $A_2$ ... $A_N$

• The first line contains two space-separated integers $N (1 ≦ N ≦ 10^5)$ and $M (1 ≦ M ≦ 10^5)$.
• The second line contains $N$ space-separated integers $A_1,$ $A_2,$ $...,$ $A_N.$ For each $i (1 ≦ i ≦ N),$ $A_i (0 ≦ A_i ≦ M)$ represents the answer of the $i^{th}$ student.

Output

If Mr. Takahashi is going to assume the correct answer to be some integer $X$, print the value of $X$ in a single line. Otherwise, print ?. Be sure to print a newline at the end of output.

Partial Points

Partial points may be awarded in this problem:

• $40$ points will be awarded for passing the test set satisfying $N ≦ 100$, $M ≦ 100.$
• Another $60$ points will be awarded for passing the test set without additional constraints.

入力例1

3 2
2 1 2

出力例1

2

入力例2

4 2
2 1 2 1

出力例2

?

入力例3

10 1
0 0 0 0 0 0 1 1 1 1

出力例3

0

入力例4

10 5
0 1 2 3 4 5 5 5 5 5

出力例4

?