#include <bits/stdc++.h>
using namespace std;
bool stB;
namespace SOL {

void debug(const char *msg, ...) {
#ifdef CLESIP
    va_list arg;
    static char pbString[512];
    va_start(arg,msg);
    vsprintf(pbString,msg,arg);
    cerr << "[DEBUG] " << pbString << "\n";
    va_end(arg);
#endif    
}

#define PASSED cerr << "PASSED " << __FUNCTION__ << " #" << __LINE__ << "\n";

using i64 = long long;
using i128 = __int128_t;
template <typename T, typename L> void chkmax(T &x, L y) { if (x < y) x = y; }
template <typename T, typename L> void chkmin(T &x, L y) { if (y < x) x = y; }

i64 work(i64 len, vector<i64> seq) {
	if (len == 1) {
		return 0;
	}
	// debug("len: %lld", len);
	// for (auto x : seq)
	// 	debug("in seq %lld", x);
	set<i64> s;
	for (auto x : seq)
		s.insert(x);
	int extra = 0;
	for (auto x : seq) {
		if (s.find(len - x + 1) == s.end()) {
			++ extra;
		}
	}
	vector<i64> nxt;
	for (int x : seq) {
		if (x <= len / 2 && s.count(len - x + 1))
			nxt.push_back(x);
	}
	return extra + work(len / 2, nxt);
}

void solve() {
	i64 n; int m;
	cin >> n >> m;
	vector<i64> seq(m);
	for (int i = 0; i < m; i ++)
		cin >> seq[i];
	cout << work(n, seq);
}

}
bool edB;
signed main() {
	// cerr << "Memory: " << (&stB - &edB) / 1024.0 / 1024.0 << "MB\n";
	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	SOL::solve();
	return 0;
}