#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
inline void mine(T1 &x, T2 y) {
  if (x > y) x = y;
}
template <typename T1, typename T2>
inline void maxe(T1 &x, T2 y) {
  if (x < y) x = y;
}
ostream &operator<<(ostream &a, const vector<long long> &b) {
  for (auto k : b) cout << k << ' ';
  return a;
}
const long long MOD = 1000000007;
const long long INF = 1000000050;
const long long BIG = (long long)2e18 + 50;
const long long MX = 200010;
const double EPS = 1e-9;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
long long n, k;
long long f(long long x) {
  if (x > n) return 0;
  long long res = 0;
  if (x % 2 == 0) res = f(x + 1);
  long long len = 0;
  while ((x << (len + 1)) <= n) {
    res += 1ll << len;
    ++len;
  }
  long long delta = n - (x << len) + 1;
  delta = min(delta, 1ll << len);
  return (res + delta);
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> n >> k;
  long long l = 0;
  long long r = n / 2 + 2;
  while (r - l > 1) {
    long long m = (r + l) / 2;
    if (f(2 * m + 1) >= k)
      l = m;
    else
      r = m;
  }
  long long res1 = 2 * l + 1;
  l = 1;
  r = n / 2 + 2;
  while (r - l > 1) {
    long long m = (r + l) / 2;
    if (f(2 * m) >= k)
      l = m;
    else
      r = m;
  }
  long long res2 = 2 * l;
  if (f(res2) < k) res2 = -INF;
  if (f(res1) < k) res1 = -INF;
  cout << max(res1, res2);
  assert(res2 != -INF || res1 != -INF);
}
