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.InputStreamReader;
import java.io.IOException;
import java.util.Arrays;
import java.io.BufferedReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author PrateekNischal
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		DZYLovesHash solver = new DZYLovesHash();
		solver.solve(1, in, out);
		out.close();
	}
}

class DZYLovesHash {
    public void solve(int testNumber, InputReader in, PrintWriter out) {
        int p = in.nextInt();
        int n = in.nextInt();
        boolean[] hash = new boolean[p];
        int res = -1;
        Arrays.fill(hash, false);
        for(int i = 1; i<=n; i++)
        {
            int x = in.nextInt()%p;
            //out.println("hash pos " + x);
            if (hash[x] == true && res == -1) {
                res = i;
            }
            else
                hash[x] = true;
        }
        out.println(res);
    }
}

class InputReader
{
    public BufferedReader reader;
    public StringTokenizer tokenizer;
    public int bufferSize = 32768;
    public InputReader(InputStream stream)
    {
        reader = new BufferedReader(new InputStreamReader(stream), bufferSize);
        tokenizer = null;
    }

    public String next()
    {
        while (tokenizer == null || !tokenizer.hasMoreTokens()){
            try{
                tokenizer = new StringTokenizer(reader.readLine());
            }catch(IOException e){throw new RuntimeException(e);}
        }
        return tokenizer.nextToken();
    }

    public int nextInt(){
        return Integer.parseInt(next());
    }
}

