#include<iostream>
#include<cstdio>
#include<set>
#define Pair pair<ll,int>
#define It set<Pair >::iterator
#define ll long long
using namespace std;
set<Pair > S[2];
int Dye(ll N,int Now)
{
	if(N==1){return 0;}
	int z=0,X=0;It y;
	for(It x=S[Now].begin();x!=S[Now].end();x++)
	{
		y=S[Now].lower_bound(make_pair(N-(x->first)+1ll,0));
		if(y==S[Now].end()||(y->first)!=N-(x->first)+1ll)
		{
			if(x->first>(N>>1)){X=N-(x->first)+1ll;}
			else{X=x->first;}
			if((x->second)==1)
			{
				S[Now^1].insert(make_pair(X,2));z++;
			}
		}
		else
		{
			if((x->first)>(N>>1)){continue;}
			X=x->first;
			if((x->second)==(y->second))
			{
				S[Now^1].insert(make_pair(X,x->second));
			}
			else
			{
				S[Now^1].insert(make_pair(X,1));
			}
		}
	}
	S[Now].clear();
	return Dye(N>>1,Now^1)+z;
}
int main()
{
	ll n=0,x=0;int m=0;
	scanf("%lld%d",&n,&m);
	for(int i=1;i<=m;i++)
	{
		scanf("%lld",&x);
		S[0].insert(make_pair(x,1));
	}
	printf("%d",Dye(n,0));
	return 0;
}