#include <bits/stdc++.h>
using namespace std;
int MOD = 1e9 + 7;
unsigned long long int power(unsigned long long int a,
                             unsigned long long int b) {
  unsigned long long int res = 1;
  a = a % MOD;
  while (b > 0) {
    if (b & 1) {
      res = (res * a) % MOD;
      b--;
    }
    a = (a * a) % MOD;
    b >>= 1;
  }
  return res;
}
unsigned long long int fermat_inv(unsigned long long int y) {
  return power(y, MOD - 2);
}
unsigned long long int gcd(unsigned long long int a, unsigned long long int b) {
  return (b == 0) ? a : gcd(b, a % b);
}
unsigned long long int min(unsigned long long int a, unsigned long long int b) {
  return (a > b) ? b : a;
}
unsigned long long int max(unsigned long long int a, unsigned long long int b) {
  return (a > b) ? a : b;
}
bool prime[1000001];
vector<int> primes;
void SieveOfEratosthenes(int n) {
  memset(prime, true, sizeof(prime));
  for (int p = 2; p * p <= n; p++) {
    if (prime[p] == true) {
      for (int i = p * p; i <= n; i += p) prime[i] = false;
    }
  }
  for (int p = 2; p < 1000001; p++)
    if (prime[p]) primes.push_back(p);
}
unsigned long long int fact[100010];
unsigned long long int finv[100010];
void factorial(int n) {
  fact[0] = 1;
  finv[0] = 1;
  for (int i = 1; i <= n; i++)
    fact[i] = fact[i - 1] * i, fact[i] %= MOD, finv[i] = fermat_inv(fact[i]);
}
unsigned long long int ncr(unsigned long long int n, unsigned long long int r) {
  if (n < r)
    return 0;
  else {
    unsigned long long int x = finv[r] * finv[n - r] % MOD;
    return fact[n] * x % MOD;
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int te = 1;
  while (te--) {
    unsigned long long int n, k;
    cin >> n >> k;
    unsigned long long int l = 1, r = (n + 1) / 2, ans = 0;
    while (l <= r) {
      unsigned long long int mid = (l + r) / 2, x = 2 * mid - 1;
      unsigned long long int cnt = 1, j = 2;
      while (j * x <= n) {
        if (n > j * x + j - 1)
          cnt += j;
        else
          cnt += n - j * x + 1;
        j *= 2;
      }
      if (cnt >= k)
        l = mid + 1, ans = max(ans, x);
      else
        r = mid - 1;
    }
    l = 1, r = n / 2;
    while (l <= r) {
      unsigned long long int mid = (l + r) / 2, x = 2 * mid;
      unsigned long long int cnt = 1 + (x + 1 <= n), j = 2;
      while (j * x <= n) {
        if (n > j * x + 2 * j - 1)
          cnt += 2 * j;
        else
          cnt += n - j * x + 1;
        j *= 2;
      }
      if (cnt >= k)
        l = mid + 1, ans = max(ans, x);
      else
        r = mid - 1;
    }
    cout << ans;
  }
}
