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.io.BufferedReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.InputStream;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeMap;
import java.util.TreeSet;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
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);
		TaskA solver = new TaskA();
                Scanner inn = new Scanner(System.in);
		solver.solve(1, in, out,inn);
		out.close();
	}
}

class TaskA {
    
    public void solve(int testNumber, InputReader in, PrintWriter out,Scanner inn) {
      /*int T = in.nextInt();
        for(int i=0;i<T;i++){
            
        }*/
        int p = in.nextInt();
        int n = in.nextInt();
        int arr[] = new int[p];
        boolean possible = true;
        for(int i=0;i<n;i++){
            int temp = in.nextInt();
            if(arr[temp%p]!=1){
                arr[temp%p]=1;
            }
            else{
                System.out.println(i+1);
                possible = false;
                break;
            }
        }
        if(possible)
            System.out.println("-1");
    }
    
    
}

class TreeNode {
    static void preOrderTraversal(TreeNode node){
        if(node.equals(null))
            return;
        System.out.println(node.idata);
        preOrderTraversal(node.left);
        preOrderTraversal(node.right);
    }
    static void postOrderTraversal(TreeNode node){
        if(node.equals(null))
            return;
        postOrderTraversal(node.left);
        postOrderTraversal(node.right);
        System.out.println(node.idata);
    }
    static void inOrderTraversal(TreeNode node){
        if(node.equals(null))
            return;
        inOrderTraversal(node.left);
        System.out.println(node.idata);
        inOrderTraversal(node.right);
    }
    String sdata = null;
    int idata = 0;
    TreeNode left = null;
    TreeNode right = null;
    TreeNode parent = null;
    TreeNode(String newstring){
        sdata= newstring;
    }
    TreeNode(int newint){
        idata= newint;
    }
    TreeNode(int newdata,String newstring){
        idata= newdata;
        sdata= newstring;
    }
    void setLeft(TreeNode node){
        left = node;
        node.parent = this;
    }
    void setRight(TreeNode node){
        right = node;
        node.parent = this;
    }
    TreeNode getBro(){
        if(hasParent()){
            if(isLeft()){
                return parent.right;
            }else{
                return parent.left;
            }
        }
        else
            return null;
    }
    boolean hasParent(){
        return !parent.equals(null);
    }
    boolean isLeft(){
        return parent.left.equals(this);
    }
    boolean isRight(){
        return parent.right.equals(this);
    }
    boolean isLeaf(){
        return this.left.equals(null)&&this.right.equals(null);
    }
    boolean isRoot(){
        return this.parent.equals(null);
    }
    TreeNode getRight(){
        if(isLeft()){
            return getBro();
        }
        else if(!parent.equals(null))
            return parent.getRight().left;
        else
            return null;
    }
    TreeNode getLeft(){
        if(isRight()){
            return getBro();
        }
        else if(!parent.equals(null))
            return parent.getLeft().right;
        else
            return null;
    }
    TreeNode getRoot(){
        if(isRoot())
            return this;
        else
            return parent.getRoot();
    }
}

class InputReader {
    public BufferedReader reader;
    public StringTokenizer tokenizer;

    public InputReader(InputStream stream) {
        reader = new BufferedReader(new InputStreamReader(stream), 32768);
        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());
    }

}