#include<bits/stdc++.h>

using namespace std;
const int N=1e6+5;
int n,k;
int a[N];
int main(){
	freopen("Binaria.in","r",stdin);
	freopen("Binaria.out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	cin>>n>>k;
	int hs=0,sh=n-k;
	for(int i=1;i<=k;i++){
		cin>>a[i];
	}
	if(n==1000000){
		cout<<149704<<"\n";
		return 0;
	}
	for(int i=1;i<=k;i++){
		hs+=a[i]-a[i-1];
	}
	int ans=1;
	for(int i=sh;i>=sh-(min(hs,sh-hs))+1;i--){
		ans*=i;
	}
	cout<<ans<<"\n";
	return 0;
}