#include <bits/stdc++.h>
using namespace std;
unsigned long long n, k;
int getlen_b(unsigned long long k) {
  int len = 0;
  for (; k; k >>= 1) len++;
  return len;
}
void print_binary(unsigned long long n) {
  int sta[100], top = 0;
  for (; n; n >>= 1) sta[++top] = n & 1;
  for (int i = top; i; i--) cout << sta[i];
  cout << endl;
}
unsigned long long calc(unsigned long long k, unsigned long long n) {
  int lenk = getlen_b(k) - 1, lenn = getlen_b(n);
  int i;
  unsigned long long res = k & 1;
  if (k & 1)
    lenk++;
  else
    k >>= 1;
  unsigned long long nn = n >> (lenn - lenk);
  for (i = 1; lenk + i < lenn; ++i) res += (1ll << i);
  if (k < nn)
    res += 1ll << (lenn - lenk);
  else if (k == nn)
    res += n - (k << (lenn - lenk)) + 1;
  return res;
}
void work() {
  cin >> n >> k;
  long long l = 1, r = n / 2, mid, res1 = -1, res2 = -1;
  while (l <= r) {
    mid = (l + r) >> 1;
    if (calc(mid * 2, n) >= k)
      l = mid + 1, res2 = mid * 2;
    else
      r = mid - 1;
  }
  l = 0, r = (n - 1) / 2;
  while (l <= r) {
    mid = (l + r) >> 1;
    if (calc(mid * 2 + 1, n) >= k)
      l = mid + 1, res1 = mid * 2 + 1;
    else
      r = mid - 1;
  }
  cout << max(res1, res2) << endl;
  return;
}
int main() {
  work();
  return 0;
}
