#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pii;
typedef pair<ll, pii> pip;
#define MAXN (ll)(1e6 + 5)

int32_t main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	ll n, m;
	cin >> n >> m;
	vector<pip> dp;
	vector<ll> pos;
	set<ll> pxx;
	for (int i = 0; i < m; i++) {
		ll x;
		cin >> x;
		x--;
		pos.push_back(x);
		pxx.insert(x);
	}
	ll p = 0;
	while ((1ll << p) != n)
		p++;
	for (auto x : pos) {
		dp.push_back(pip(x, pii(1, 0)));
	}
	for (auto x : pos)
		if (!pxx.count(n - x - 1))
			dp.push_back(pip(n - x - 1, pii(0, 1)));
	sort(all(dp));
	auto at = [&](ll x) {
		int pos = lower_bound(all(dp), pip(x, pii(0, 0))) - dp.begin();
		return dp[pos].second;
	};

	for (int i = 0; i < p; i++) {
		vector<pip> tp;
		for (auto p : dp) {
			if (p.first < n / 2) {
				pii xxx = at(n - p.first - 1);
				ll v0 = p.second.first + xxx.first;
				ll v1 = p.second.second + xxx.second;
				v0 = min(v0, v1 + 1);
				v1 = min(v1, v0 + 1);
				tp.push_back(pip(p.first, pii(v0, v1)));
			}
		}
		n /= 2;
		set<ll> pxx;
		for (auto x : tp)
			pxx.insert(x.first);
		for (auto x : pxx)
			if (!pxx.count(n - x - 1))
				tp.push_back(pip(n - x - 1, pii(0, 1)));
		dp.clear();
		dp = tp;
	}

	cout << min(dp[0].second.first, dp[0].second.second) << "\n";

	return 0;
}