#include <bits/stdc++.h>
using namespace std;
template <typename T>
inline bool upmin(T &x, T y) {
  return y <= x ? x = y, 1 : 0;
}
template <typename T>
inline bool upmax(T &x, T y) {
  return x <= y ? x = y, 1 : 0;
}
const long double eps = 1e-9;
const long double pi = acos(-1);
const int oo = 1 << 30;
const long long loo = 1ll << 60;
const int MAXN = 200005;
const int MAXM = 2000005;
const int MX = 5000;
const int mods = 998244353;
const int SZ = 131;
const int inv2 = (mods + 1) >> 1;
const int INF = 0x3f3f3f3f;
namespace FastIO {
constexpr int SIZE = (1 << 21) + 1;
int num = 0, f;
char ibuf[SIZE], obuf[SIZE], que[65], *iS, *iT, *oS = obuf,
                                                *oT = obuf + SIZE - 1, c;
inline void flush() {
  fwrite(obuf, 1, oS - obuf, stdout);
  oS = obuf;
}
inline void putc(char c) {
  *oS++ = c;
  if (oS == oT) flush();
}
inline void getc(char &c) {
  for (c = (iS == iT ? (iT = ((iS = ibuf) + fread(ibuf, 1, SIZE, stdin)),
                       (iS == iT ? EOF : *iS++))
                     : *iS++);
       !isalpha(c) && c != EOF;
       c = (iS == iT ? (iT = ((iS = ibuf) + fread(ibuf, 1, SIZE, stdin)),
                       (iS == iT ? EOF : *iS++))
                     : *iS++))
    ;
}
inline void reads(char *st) {
  char c;
  int n = 0;
  getc(st[++n]);
  for (c = (iS == iT ? (iT = ((iS = ibuf) + fread(ibuf, 1, SIZE, stdin)),
                       (iS == iT ? EOF : *iS++))
                     : *iS++);
       isalpha(c);
       c = (iS == iT ? (iT = ((iS = ibuf) + fread(ibuf, 1, SIZE, stdin)),
                       (iS == iT ? EOF : *iS++))
                     : *iS++))
    st[++n] = c;
  st[++n] = '\0';
}
template <class I>
inline void read(I &x) {
  for (f = 1, c = (iS == iT ? (iT = ((iS = ibuf) + fread(ibuf, 1, SIZE, stdin)),
                              (iS == iT ? EOF : *iS++))
                            : *iS++);
       c < '0' || c > '9';
       c = (iS == iT ? (iT = ((iS = ibuf) + fread(ibuf, 1, SIZE, stdin)),
                       (iS == iT ? EOF : *iS++))
                     : *iS++))
    if (c == '-') f = -1;
  for (x = 0; c >= '0' && c <= '9';
       c = (iS == iT ? (iT = ((iS = ibuf) + fread(ibuf, 1, SIZE, stdin)),
                       (iS == iT ? EOF : *iS++))
                     : *iS++))
    x = (x << 3) + (x << 1) + (c & 15);
  x *= f;
}
template <class I>
inline void print(I x) {
  if (x < 0) putc('-'), x = -x;
  if (!x) putc('0');
  while (x) que[++num] = x % 10 + 48, x /= 10;
  while (num) putc(que[num--]);
}
inline void putstr(string st) {
  for (int i = 0; i < (int)st.size(); ++i) putc(st[i]);
}
struct Flusher_ {
  ~Flusher_() { flush(); }
} io_Flusher_;
}  // namespace FastIO
using FastIO ::print;
using FastIO ::putc;
using FastIO ::putstr;
using FastIO ::read;
using FastIO ::reads;
int A[1 << 18], flag[1 << 18], f[18][1 << 18][2][2], n, K;
signed main() {
  read(n), read(K);
  for (int i = 1; i <= K; ++i) read(A[i]), --A[i], flag[A[i]] = 1;
  memset(f, -INF, sizeof f);
  for (int i = 0; i < (1 << (n - 1)); ++i)
    f[1][i][flag[i << 1]][flag[i << 1 | 1]] = flag[i << 1] | flag[i << 1 | 1],
                                        f[1][i][flag[i << 1 | 1]]
                                         [flag[i << 1]] =
                                             flag[i << 1] | flag[i << 1 | 1];
  for (int i = 2; i <= n; ++i) {
    for (int j = 0; j < 1 << (n - i); ++j)
      for (int p = 0; p < 2; ++p)
        for (int q = 0; q < 2; ++q)
          for (int x = 0; x < 2; ++x)
            for (int y = 0; y < 2; ++y) {
              int t = f[i - 1][j << 1][p][q] + f[i - 1][j << 1 | 1][x][y];
              upmax(f[i][j][p | x][q | y], t + (p | x) + ((q | y) << 1));
              if (p | x)
                upmax(f[i][j][p + x - 1][1], t + (p | x) + (q | y) + 1);
            }
  }
  int ans = 0;
  for (int p = 0; p < 2; ++p)
    for (int q = 0; q < 2; ++q) upmax(ans, f[n][0][p][q] + (p | q));
  print(ans);
  return 0;
}
