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;
ifstream fin("frac1.in");
ofstream fout("frac1.out");
class compare : public std::binary_function<double, double, bool> {
 public:
  compare(double arg = 1e-7) : e(arg) {}
  bool operator()(const double &left, const double &right) const {
    return (abs(left - right) > e) && (left < right);
  }
  double e;
};
inline long long myabs(long long a) { return (a < 0) ? -a : a; }
inline int d_compare(double x, double y) {
  return (fabs(x - y) <= 1e-7) ? 0 : (x > y) ? 1 : -1;
}
inline int mod(long long x, int y) {
  if (y == 0) return x;
  if (x < 0) x = -x;
  if (x >= y) x %= y;
  return x;
}
inline int cmod(int x, int y) {
  if (y == 0) return x;
  if (x < 0) x += (abs(x) / y + 1) * y;
  if (x >= y) x = x % y;
  return x;
}
int Bcount(int mask) {
  int n = 0;
  while (mask) n += ((mask & -mask) != 0), mask &= ~(mask & -mask);
  return n;
}
inline bool Bstate(int mask, int idx) { return (mask & (1 << idx)); }
inline int B1(int mask, int idx) { return mask | (1 << idx); }
inline int B0(int mask, int idx) { return mask & ~(1 << idx); }
inline int drift(int mask, int n) { return mask & ((1 << n) - 1); }
void debugmask(int mask, int n) {
  for (int i = 0; i < n; i++) cout << Bstate(mask, i);
}
int dr[8] = {0, 0, -1, 1, -1, 1, -1, 1}, dc[8] = {-1, 1, 0, 0, 1, -1, -1, 1};
template <typename Ty>
void clear(Ty &q) {
  Ty empty;
  swap(q, empty);
}
int main() {
  int p, n;
  cin >> p >> n;
  int flag = -1;
  bool arr[300] = {0};
  for (int i = 0; i < n; i++) {
    int temp;
    cin >> temp;
    temp %= p;
    if (flag == -1 && arr[temp]) flag = i;
    arr[temp] = 1;
  }
  if (flag != -1)
    cout << flag + 1 << endl;
  else
    cout << -1 << endl;
  return 0;
}
