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
#include <bits/stdc++.h>
using namespace std;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
long long powmod(long long a, long long b, long long mod) {
  if (b == 0 || a == 1) {
    if (mod == 1)
      return 0;
    else
      return 1;
  }
  if (b % 2 == 0) {
    long long k = powmod(a, b / 2, mod);
    return (k * k) % mod;
  } else {
    long long k = powmod(a, b / 2, mod);
    return ((k * k) % mod * a) % mod;
  }
}
long long gcd(long long a, long long b) {
  if (a == 0) return b;
  if (b == 0) return a;
  if (a > b)
    return gcd(a % b, b);
  else
    return gcd(b % a, a);
}
long long prime(long long p) {
  for (long long i = 2; i * i <= p; i++) {
    if (p % i == 0 && i < p) return i;
  }
  return 1;
}
long long inv(long long a, long long mod) { return powmod(a, mod - 2, mod); }
long long random_modul() {
  uniform_int_distribution<long long> u1(1e10, 1e11);
  long long pepega = u1(rnd);
  while (prime(pepega) != 1) pepega = u1(rnd);
  return pepega;
}
long long a[102], n, m, i, p, j;
void solve() {
  long long k, a;
  cin >> k >> a;
  map<long long, long long> mem;
  for (long long i = 1; i <= a; i++) {
    long long x;
    cin >> x;
    mem[x % k]++;
    if (mem[x % k] == 2) {
      cout << i;
      return;
    }
  }
  cout << -1;
  return;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long tututu;
  tututu = 1;
  for (long long qwerty = 0; qwerty < tututu; qwerty++) solve();
  return 0;
}
