#include<bits/stdc++.h>
#define Gc() getchar() 
#define Me(x,y) memset(x,y,sizeof(x))
#define Mc(x,y) memcpy(x,y,sizeof(x))
#define d(x,y) ((m)*(x-1)+(y))
#define R(n) (rnd()%(n)+1)
#define Pc(x) putchar(x)
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
using namespace std;using ll=long long;using db=double;using lb=long db;using ui=unsigned;using ull=unsigned long long;using pii=pair<int,int>;using LL=__int128;
const int N=5e5+5,M=(1<<16)+5,K=(1<<25)+5,mod=1e9+7,Mod=mod-1;const db eps=1e-9;const int INF=1e9+7;mt19937 rnd(time(0));
int m;ll n;
map<ll,int> f;
int dfs(ll x){
	if(x==1) return 0;
	vector<ll> scc;
	for(auto i:f) scc.emplace_back(i.fi>x/2?x-i.fi+1:i.fi);
	sort(scc.begin(),scc.end());scc.erase(unique(scc.begin(),scc.end()),scc.end());
	int ans=0;
	for(ll i:scc){
		int w1=f[i],w2=f[x-i+1];
		if(w1==w2) ;
		else if(w1==-1&&w2==-1) ;
		else if(w1==-1||w2==-1){
			if(w1==-1) f[i]=f[x-i+1];
		}else f[i]=-1,ans++;
		f.erase(x-i+1);
	}
	// cerr<<x<<' '<<ans<<'\n';
	return ans+dfs(x/2);
}
void Solve(){
	int i,j;scanf("%lld%d",&n,&m);
	for(i=1;i<=n;i++){
		ll x;scanf("%lld",&x);f[x]=1;
	}
	printf("%lld\n",dfs(n));
}
int main(){
	int t=1;
	// scanf("%d",&t);
	while(t--) Solve();
	cerr<<clock()*1.0/CLOCKS_PER_SEC<<'\n';
}