#include <fstream>
#include <bitset>

using namespace std;

ifstream cin("grigo.in");
ofstream cout("grigo.out");

bitset<100001> b;
const long long MOD = 1'000'000'007;

int main() {
    int n, m;
    cin >> n >> m;
    for (int i = 0 ; i < m ; ++i) {
        int x; cin >> x;
        b[x] = true;
    }
    long long ans = 1;
    for (int i = 1 ; i <= n ; ++i) {
        if (!b[i]) ans = ans * (i - 1) % MOD;
    }
    cout << ans;
    return 0;
}