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.File;
import java.io.FileReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.*;

import static java.util.Collections.reverseOrder;

/**
 * Created with IntelliJ IDEA.
 * User: AUtemuratov
 * Date: 07.04.14
 * Time: 15:43
 * To change this template use File | Settings | File Templates.
 */
public class Main {
    static FastReader fr = new FastReader(new BufferedReader(new InputStreamReader(System.in)));
    static PrintWriter pw = new PrintWriter(System.out);
    static int p,n,m,cnt,ans;
    static int max = Integer.MIN_VALUE;
    static int min = Integer.MAX_VALUE;
    static int maxn = (int)1e5+111;
    static int a[] = new int [maxn];
    static boolean u[] = new boolean[maxn];
    static ArrayList<Integer> arr = new ArrayList<>();
    
    public static void main(String[] args) throws Exception {
    
        p = fr.nextInt();
        n = fr.nextInt();
        
        for (int i=1; i<=n; i++) {
            int t = fr.nextInt();
            int num = t%p;
            check(num,i);
            arr.add(num);
        }
        pw.println(-1);
        pw.close(); 
    }

    private static void check(int num,int eq) {
        for (int i=0; i<arr.size(); i++) {
            if (arr.get(i)==num) {
                pw.println(eq);
                pw.close();
                System.exit(0);
            }
        }
    }

    
}

class Pair {
    public int l,r;
    public Pair(int l, int r) {
        this.l = l;
        this.r = r;
    }
}

class FastReader {

    BufferedReader bf;
    StringTokenizer tk = null;
    String DELIM = " ";

    public FastReader(BufferedReader bf) {
        this.bf = bf;
    }

    public String nextToken() throws Exception {

        if(tk==null || !tk.hasMoreTokens()) {
            tk = new StringTokenizer(bf.readLine(),DELIM);
        }
        return tk.nextToken();
    }

    public int nextInt() throws Exception {
        return Integer.parseInt(nextToken());
    }

    public int nextLong() throws Exception {
        return Integer.parseInt(nextToken());
    }

    public int nextDouble() throws Exception {
        return Integer.parseInt(nextToken());
    }
}