/*
Things to notice:
1. do not calculate useless values
2. do not use similar names
 
Things to check:
1. submit the correct file
2. time (it is log^2 or log)
3. memory
4. prove your naive thoughts 
5. long long
6. corner case like n=0,1,inf or n=m
7. check if there is a mistake in the ds or other tools you use
8. fileio in some oi-contest

9. module on time 
10. the number of a same divisor in a math problem
11. multi-information and queries for dp and ds problems
*/
#include<bits/stdc++.h>
using namespace std;
#define int long long
#define fi first
#define se second
#define pii pair<long long,long long>
#define mp make_pair
#define pb push_back
const int mod=998244353;
const int inf=0x3f3f3f3f;
const int INF=1e18;
int n,m,tot;
vector <int> calc(vector <int> L,vector <int> R,vector <int> fr)
{
	sort(L.begin(),L.end()),sort(R.begin(),R.end());
	vector <int> vec;
	for(int i=0;i<L.size();i++)
	{
		int x=n-L[i]+1;
		int p=lower_bound(R.begin(),R.end(),x)-R.begin();
		if(p<R.size()&&R[p]==x) continue;
		int flg1=0,flg2=0;
		p=lower_bound(fr.begin(),fr.end(),x)-fr.begin();
		if(p<fr.size()&&fr[p]==x) flg1=1;
		p=lower_bound(fr.begin(),fr.end(),n-x+1)-fr.begin();
		if(p<fr.size()&&fr[p]==x) flg2=1;
		if(flg1&&flg2) vec.pb(L[i]);
		else if(flg1+flg2==0) tot++,vec.pb(L[i]);
		
	}
	for(int i=0;i<R.size();i++)
	{
		int x=n-R[i]+1;
		int p=lower_bound(L.begin(),L.end(),x)-L.begin();
		if(p<L.size()&&L[p]==x) continue;
		int flg1=0,flg2=0;
		p=lower_bound(fr.begin(),fr.end(),x)-fr.begin();
		if(p<fr.size()&&fr[p]==x) flg1=1;
		p=lower_bound(fr.begin(),fr.end(),n-x+1)-fr.begin();
		if(p<fr.size()&&fr[p]==x) flg2=1;
		
		if(flg1&&flg2) vec.pb(n-R[i]+1);
		else if(flg1+flg2==0) tot++,vec.pb(n-R[i]+1);
	}
	sort(vec.begin(),vec.end());
	return vec;
}
void solve()
{
	cin>>n>>m;
	vector <int> vec;
	while(m--)
	{
		int x;
		cin>>x;
		vec.pb(x);
	}
	vector <int> fr;
	while(n>1)
	{
		vector <int> L,R;
		for(int i=0;i<vec.size();i++) 
		{
			if(vec[i]<=n/2) L.pb(vec[i]);
			else R.pb(vec[i]);
		}
		fr=calc(L,R,fr);
		vec=L;
		n/=2;
	}
	cout<<tot<<"\n";
}
signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	int _=1;
//	cin>>_;
	while(_--) solve();
	return 0;
}