// Source: https://usaco.guide/general/io

#include <cstdlib>
#include <cstring>
#include <iostream>
#include <vector>
#include <chrono>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <string>
#include <bitset>
#include <random>

#define int long long
#define sz(x) (int) x.size()
#define all(x) x.begin(), x.end()

using namespace std;

signed main() {
    cin.tie(0) -> sync_with_stdio(false);

    int N, M; cin >> N >> M;

	map<int, int> mmap;

	for (int i = 0; i < M; i++) {
		int a; cin >> a; mmap[a] = 1;
	}

	map<int, int> nxt;

	int cost = 0;

	while (N > 1) {
		nxt.clear();

		// for (auto p : mmap) {
		// 	cout << p.first << " " << p.second << "\n";
		// }

		// cout << "\n";

		// do halving
		for (auto it = mmap.begin(); it != mmap.end(); it = next(it)) {
			int add = min(it->first, N - it->first + 1);

			if (mmap.count(N - it->first + 1)) {
				if (it->second == 1) {
					if (mmap[N - it->first + 1] == 1) {
						nxt[add] = 1;
					} else { // mmap[N - it->first] == 2
						nxt[add] = 1;
					}
				} else { // it->second == 2
					if (mmap[N - it->first + 1] == 1) {
						nxt[add] = 1;
					} else { // mmap[N - it->first] == 2
						nxt[add] = 2;
					}
				}
			} else {
				if (it->second == 1) {
					nxt[add] = 2; cost++;
				} else { // it->second == 2
					nxt[add] = 0;
				}
			}
		}

		swap(nxt, mmap);
		N /= 2LL;
	}

	cout << cost << "\n";
}