#include <bits/stdc++.h>
using namespace std;
template <class T>
bool umin(T& a, const T& b) {
  return a > b ? a = b, true : false;
}
template <class T>
bool umax(T& a, const T& b) {
  return a < b ? a = b, true : false;
}
template <long long sz>
using tut = array<long long, sz>;
const long long N = (1 << 17) + 5;
const long long mod = 1e9 + 7;
const long long inf = 1e18;
const long double Pi = acos(-1);
void add(long long& a, long long b) { a = (a + b) % mod; }
void sub(long long& a, long long b) { a = ((a - b) % mod + mod) % mod; }
void mul(long long& a, long long b) { a = (a * 1ll * b) % mod; }
long long n, m, k, t, q, ans, res, a[N];
long long dp[4 * N][2][2], used[N];
long long rec(long long l, long long r, long long u, long long d, long long x) {
  long long& res = dp[x][u][d];
  if (res != -1) return res;
  if (l + 1 == r - 1) {
    if (u + d != used[l] + used[l + 1])
      res = -2;
    else
      res = (used[l] | used[l + 1]);
    return res;
  }
  res = -2;
  long long m = (l + r) >> 1;
  for (long long ulx = 0; ulx < 2; ulx++) {
    for (long long dlx = 0; dlx < 2; dlx++) {
      for (long long urx = 0; urx < 2; urx++) {
        for (long long drx = 0; drx < 2; drx++) {
          long long lx = rec(l, m, ulx, dlx, x << 1),
                    rx = rec(m, r, urx, drx, x << 1 | 1);
          if (lx == -2 || rx == -2) continue;
          if ((ulx == u || urx == u) && (dlx == d || drx == d)) {
            long long add = 0;
            if (ulx == u) {
              if (dlx == d) umax(add, (dlx | urx));
              if (drx == d) umax(add, (drx | urx));
            }
            if (urx == u) {
              if (dlx == d) umax(add, (dlx | ulx));
              if (drx == d) umax(add, (drx | ulx));
            }
            umax(res, lx + rx + (ulx | urx) + (dlx | drx) + add);
          }
          if (ulx == u && (urx == d))
            umax(res, lx + rx + (ulx | urx) + (dlx | drx) + (urx | dlx | drx));
          if (urx == u && (ulx == d))
            umax(res, lx + rx + (ulx | urx) + (dlx | drx) + (ulx | dlx | drx));
        }
      }
    }
  }
  return res;
}
void solve(long long t_case) {
  memset(dp, -1, sizeof dp);
  cin >> n >> k;
  for (long long i = 1; i <= k; i++) {
    long long x;
    cin >> x;
    used[--x]++;
  }
  for (long long i = 0; i < 2; i++)
    for (long long j = 0; j < 2; j++)
      umax(res, rec(0, (1 << n), i, j, 1) + (i | j));
  cout << res << "\n";
}
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  if (0) {
    long long t;
    cin >> t;
    for (long long t_case = 1; t_case <= t; t_case++) solve(t_case);
  } else
    solve(1);
  return 0;
}
