#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <cassert>
#include <iomanip>
#include <iostream>
#include <algorithm>
//#include <unordered_set>
//#include <unordered_map>

#define pii pair<int, int>

#define pb push_back
#define mp make_pair

#define f first
#define s second

using namespace std;


typedef long double ld;
typedef long long ll;


const ld PI = acos(-1);
const ld EPS = 1e-6;

const int MOD = (int) 1e9 + 7;
const int N = (int) 2e5 + 7;

const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, -1, 0, 1};

int mod, n;
int a[N];
int b[N];
map<int, int> used;

int main() {
  #ifdef LOCAL
  freopen("in.txt", "r", stdin);
  //freopen("out.txt", "w", stdout);
  #endif

  scanf("%d%d", &mod, &n);
  int sum = 0;
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    sum = (sum + a[i]) % mod;
    used[a[i]] = 1;
  }
  sort(a + 1, a + n + 1);
  if (n == 1) {
    cout << a[1] << ' ' << 0;
    return 0;
  }
  for (int i = 2; i <= n; i++) {
    int d = (a[i] - a[1] + mod) % mod;
    int len = 1;
    int cur = a[1];
    int x;
    for (x = (cur + d) % mod; len <= n && used[x]; x = (x + d) % mod) len++;
    for (x = (cur - d + mod) % mod; len <= n && used[x]; x = (x - d + mod) % mod) len++;
    if (len >= n) {
      cout << (x + d) % mod << ' ' << d;
      return 0;
    }
  }
  swap(a[1], a[2]);
  for (int i = 2; i <= n; i++) {
    int d = (a[i] - a[1] + mod) % mod;
    int len = 1;
    int cur = a[1];
    int x;
    for (x = (cur + d) % mod; len <= n && used[x]; x = (x + d) % mod) len++;
    for (x = (cur - d + mod) % mod; len <= n && used[x]; x = (x - d + mod) % mod) len++;
    if (len >= n) {
      cout << (x + d) % mod << ' ' << d;
      return 0;
    }
  }
  cout << -1;
  return 0;
}