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.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
import java.util.TreeSet;

/*07:05:45PM

 String x =sc.next();
 char inp [] = x.toCharArray();
 SimpleDateFormat displayFormat = new SimpleDateFormat("HH:mm");
 SimpleDateFormat parseFormat = new SimpleDateFormat("hh:mm a");
 Date date = parseFormat.parse(x.substring(0, 5)+" "+x.substring(8, 10));
 System.out.println(displayFormat.format(date)+":"+x.substring(6, 8));
 */

public class Main {
	
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int p =sc.nextInt() , n =sc.nextInt();
		TreeSet<Integer> ts = new TreeSet<Integer>();
		int cnt = 1;
		while(n-->0)
		{
			int x = sc.nextInt();
			if(ts.contains(x%p)){System.out.println(cnt);return;}
			ts.add(x%p);
			cnt++;
		}
		System.out.println(-1);
	}
}

class Triple {
	long x, y, z;

	public Triple(long a, long b, long c) {
		x = a;
		y = b;
		z = c;
	}
}

class Pair implements Comparable<Pair> {
	int w, h;

	Pair(int f, int b) {
		w = f;
		h = b;

	}

	@Override
	public int compareTo(Pair p) {
		// TODO Auto-generated method stub
		return h == p.h ? w - p.w : p.h - h;
	}

}

class Scanner {
	StringTokenizer st;
	BufferedReader br;

	public Scanner(InputStream s) {
		br = new BufferedReader(new InputStreamReader(s));
	}

	public String next() throws IOException {
		while (st == null || !st.hasMoreTokens())
			st = new StringTokenizer(br.readLine());
		return st.nextToken();
	}

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

	public long nextLong() throws IOException {
		return Long.parseLong(next());
	}

	public String nextLine() throws IOException {
		return br.readLine();
	}

	public double nextDouble() throws IOException {
		String x = next();
		StringBuilder sb = new StringBuilder("0");
		double res = 0, f = 1;
		boolean dec = false, neg = false;
		int start = 0;
		if (x.charAt(0) == '-') {
			neg = true;
			start++;
		}
		for (int i = start; i < x.length(); i++)
			if (x.charAt(i) == '.') {
				res = Long.parseLong(sb.toString());
				sb = new StringBuilder("0");
				dec = true;
			} else {
				sb.append(x.charAt(i));
				if (dec)
					f *= 10;
			}
		res += Long.parseLong(sb.toString()) / f;
		return res * (neg ? -1 : 1);
	}

	public boolean ready() throws IOException {
		return br.ready();
	}

}