#include <bits/stdc++.h>
using namespace std;
int n, m;
int a[100000] = {0};
int adiff[100000];
bool flag = false;
long ans = 1;
void solve() {
  for (int i = 0; i <= m; i++) {
    if (adiff[i] - 1 >= 0) {
      ans *= pow(2, adiff[i] - 1);
    }
  }
}
int main() {
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    cin >> a[i];
    if (i > 0 && a[i] - a[i - 1] == 1) {
      cout << 0 << endl;
      return 0;
    }
    if (i == 0) {
      adiff[i] = a[i] - 1;
    } else {
      adiff[i] = a[i] - a[i - 1] - 1;
    }
  }
  adiff[m] = n - a[m - 1] - 1;
  solve();
  cout << ans % 1000000007 << endl;
}
