#include <bits/stdc++.h>
using namespace std;
long long n, m, a[100010];
map<long long, bool> app;
bool comp;
long long binpow(long long a, long long b) {
  long long res = 1;
  while (b) {
    if (b & 1) {
      res *= a;
      res %= m;
    }
    a *= a;
    a %= m;
    b >>= 1;
  }
  return res;
}
void sol() {
  long long kd, nmink = 0, d, x;
  kd = abs(a[0] - a[1]);
  for (long long i = 0; i < n; ++i) {
    nmink += app[(a[i] + kd) % m];
  }
  d = (kd * binpow(n - nmink, m - 2)) % m;
  x = a[0];
  while (app[(x - d + m) % m]) {
    x = (x - d + m) % m;
  }
  long long res = x, cnt = 0;
  while (app[(x + d) % m]) {
    x = (x + d) % m;
    ++cnt;
  }
  if (cnt == n - 1) {
    if (comp) {
      res = (x + d) % m;
    }
    cout << res << " " << d;
  } else {
    cout << -1;
  }
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cin >> m >> n;
  for (long long i = 0; i < n; ++i) {
    cin >> a[i];
    app[a[i]] = 1;
  }
  if (n == 1 or n == m) {
    cout << a[0] << " 1\n";
    return 0;
  }
  if (n == m - 1) {
    sort(a, a + n);
    for (long long i = 0; i < n; ++i) {
      if (a[i + 1] - a[i] > 1) {
        cout << a[i + 1] << " 1\n";
        return 0;
      }
    }
    cout << a[0] << " 1\n";
    return 0;
  }
  if (2 * n > m) {
    comp = 1;
    n = 0;
    for (long long i = 0; i < m; ++i) {
      if (!app[i]) {
        a[n] = i;
        n++;
      }
    }
    for (long long i = 0; i < m; ++i) {
      app[i] = 0;
    }
    for (long long i = 0; i < n; ++i) {
      app[a[i]] = 1;
    }
  }
  sol();
}
