DZY has a hash table with p buckets, numbered from 0 to p - 1. He wants to insert n numbers, in the order they are given, into the hash table. For the i-th number xi, DZY will put it into the bucket numbered h(xi), where h(x) is the hash function. In this problem we will assume, that h(x) = x mod p. Operation a mod b denotes taking a remainder after division a by b.

However, each bucket can contain no more than one element. If DZY wants to insert an number into a bucket which is already filled, we say a "conflict" happens. Suppose the first conflict happens right after the i-th insertion, you should output i. If no conflict happens, just output -1.

Input

The first line contains two integers, p and n (2 ≤ p, n ≤ 300). Then n lines follow. The i-th of them contains an integer xi (0 ≤ xi ≤ 109).

Output

Output a single integer — the answer to the problem.

Examples

Input

10 5
0
21
53
41
53


Output

4


Input

5 5
0
1
2
3
4


Output

-1
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.security.acl.LastOwnerException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Random;
import java.util.StringTokenizer;

import javax.lang.model.type.PrimitiveType;

public class Main
{

	private static BufferedWriter out;

	public static void main(String[] args) throws IOException
	{
		// The input and output streams
		boolean file = false;
		BufferedReader in;
		if (file)
			in = new BufferedReader(new FileReader("input.txt"), 32768);
		else
			in = new BufferedReader(new InputStreamReader(System.in), 32768);
		out = new BufferedWriter(new OutputStreamWriter(System.out));
		StringTokenizer tok;

		// take input
		tok = new StringTokenizer(in.readLine());
		int p  =Integer.parseInt(tok.nextToken());
		int n  =Integer.parseInt(tok.nextToken());
		HashSet<Integer> found = new HashSet<>();
		int curr = 1;
		for (int i = 0; i < n; i++)
		{
			Integer x = Integer.parseInt(in.readLine());
			int h = x % p;
			if (found.contains(h))
			{
				System.out.println(curr);
				return;
			}
			else
				found.add(h);
			curr ++;
		}
		
		System.out.println(-1);
		
		out.flush();

	}

}