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.util.Scanner;

/**
 * Noli nocere!
 */
public class A {

/*  static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        FastScanner(File f) {
            try {
                br = new BufferedReader(new FileReader(f));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }

        String next() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        boolean hasNext() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    if(br.ready()) {
                        st = new StringTokenizer(br.readLine());
                    }
                    else {
                        return false;
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.hasMoreTokens();
        }

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

//  static FastScanner in;
    static Scanner in;
//  static PrintWriter out;

    public static void main(String[] args) {
    /*  try {
            in = new FastScanner(new File(""));
            out = new PrintWriter("");
        } catch (IOException e) {
            e.printStackTrace();
        }     */
        in = new Scanner(System.in);

        int p = in.nextInt();
        int n = in.nextInt();
        boolean[] table = new boolean[p];
        for (int i = 1; i < p; i++) {
            table[i] = false;
        }
        int i;
        int a;
        for(i = 1; i < n + 1; i++) {
            a = in.nextInt();
            if (table[a % p]) {
                break;
            }
            else {
                table[a % p] = true;
            }
        }
        if(i < n + 1) {
            System.out.println(i);
        }
        else {
            System.out.println(-1);
        }

        System.out.close();
    }
}

