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.*;

public class Task447A {

    public static void main(String... args) throws NumberFormatException,
            IOException {
        Solution.main(System.in, System.out);
    }

    static class Scanner {

        private final BufferedReader br;
        private String[] cache;
        private int cacheIndex;

        Scanner(InputStream is) {
            br = new BufferedReader(new InputStreamReader(is));
            cache = new String[0];
            cacheIndex = 0;
        }

        int nextInt() throws IOException {
            if (cacheIndex >= cache.length) {
                cache = br.readLine().split(" ");
                cacheIndex = 0;
            }
            return Integer.parseInt(cache[cacheIndex++]);
        }

        long nextLong() throws IOException {
            if (cacheIndex >= cache.length) {
                cache = br.readLine().split(" ");
                cacheIndex = 0;
            }
            return Long.parseLong(cache[cacheIndex++]);
        }

        String next() throws IOException {
            if (cacheIndex >= cache.length) {
                cache = br.readLine().split(" ");
                cacheIndex = 0;
            }
            return cache[cacheIndex++];
        }

        void close() throws IOException {
            br.close();
        }

    }

    static class Solution {

        public static void main(InputStream is, OutputStream os)
                throws NumberFormatException, IOException {
            PrintWriter pw = new PrintWriter(os);
            Scanner sc = new Scanner(is);

            int p = sc.nextInt();
            int n = sc.nextInt();

            boolean h[] = new boolean[p];

            for (int i = 0; i < n; i++) {
                int xi = sc.nextInt() % p;
                if (h[xi]) {
                    pw.println(i + 1);
                    pw.flush();
                    sc.close();
                    return;
                }
                h[xi] = true;
            }

            pw.println(-1);
            pw.flush();
            sc.close();
        }
    }

}