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.FileReader;
import java.io.BufferedReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.Writer;
import java.util.StringTokenizer;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author Agostinho Junior (junior94)
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		OutputWriter out = new OutputWriter(outputStream);
		TaskA solver = new TaskA();
		solver.solve(1, in, out);
		out.close();
	}
}

class TaskA {
	OutputWriter out;
	InputReader in;
	public void solve(int testNumber, InputReader in, OutputWriter out) {
		this.in = in; this.out = out;
		int p = in.readInt();
		int n = in.readInt();
		boolean[] filled = new boolean[p];
		for (int i = 1; i <= n; i++) {
			int x = in.readInt() % p;
			if (filled[x]) {
				out.print(i);
				return;
			} else {
				filled[x] = true;
			}
		}
		out.print(-1);
	}
}

class OutputWriter {
	private PrintWriter output;
	public OutputWriter() {
		this(System.out);
	}
	public OutputWriter(OutputStream out) {
		output = new PrintWriter(out);
	}
	public OutputWriter(Writer writer) {
		output = new PrintWriter(writer);
	}
	public void print(Object o) {
		output.print(o);
	}

	public void close() {
		output.close();
	}
}

class InputReader {
	private BufferedReader input;
	private StringTokenizer line = new StringTokenizer("");
	public InputReader() {
		this(System.in);
	}
	public InputReader(InputStream in) {
		input = new BufferedReader(new InputStreamReader(in));
	}
	public InputReader(String s) {
		try {
			input = new BufferedReader(new FileReader(s));
		} catch(IOException io) { io.printStackTrace(); System.exit(0);}
	}
	public void fill() {
		try {
			if(!line.hasMoreTokens()) line = new StringTokenizer(input.readLine());
		} catch(IOException io) { io.printStackTrace(); System.exit(0);}
	}

	public int readInt() {
		fill();
		return Integer.parseInt(line.nextToken());
	}
}

