/*
    IN THE NAME OF GOD
*/
#include <bits/stdc++.h>

// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

using namespace std;

typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef long double ld;

#define F                                      first
#define S                                      second
#define Mp                                     make_pair
#define pb                                     push_back
#define pf                                     push_front
#define size(x)                                ((ll)x.size())
#define all(x)                                 (x).begin(),(x).end()
#define kill(x)		                           cout << x << '\n', exit(0);
#define fuck(x)                                cout << "(" << #x << " , " << x << ")" << endl
#define endl                                   '\n'

const int N = 3e5+23, lg = 18;
ll Mod = 1e9+7; //998244353;

inline ll MOD(ll a, ll mod=Mod) {a%=mod; (a<0)&&(a+=mod); return a;}
inline ll poww(ll a, ll b, ll mod=Mod) {
    ll ans = 1;
    a=MOD(a, mod);
    while (b) {
        if (b & 1) ans = MOD(ans*a, mod);
        b >>= 1;
        a = MOD(a*a, mod);
    }
    return ans;
}

ll t, n, m, a[N], cnt;
unordered_map<ll, int> mp;

int main () {
	ios_base::sync_with_stdio(false), cin.tie(0);

    cin>>n>>m;
    for(int i=1; i<=m; i++) {
        cin>>a[i]; mp[a[i]] = 1;
    }

    ll ans = 0;
    while(n > 1) {
        for(auto it : mp) {
            if(mp.find(n-it.F+1) == mp.end()) mp[n-it.F+1] = 0;
        }
        unordered_map<ll, int> mp2;
        for(auto it : mp) {
            if(it.F <= n/2ll) {
                int x = mp[n-it.F+1];
                if(it.S == x) mp2[it.F] = it.S;
                else {
                    if(x == -1 || it.S == -1) {
                        mp2[it.F] = max(x, it.S);
                    } else {
                        ans++; mp2[it.F] = -1;
                    }
                }
            }
        }
        mp = mp2; n/=(2ll);
    }

    cout<<ans<<endl;

	return 0;
}