#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;

using isize = size_t;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128_t;
using u128 = __uint128_t;
using f64 = long double;
using p2 = pair<i64, i64>;
using el = tuple<i64, i64, i64>;
using mint = atcoder::modint998244353;

void _main();
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(18);
  _main();
}

i64 pow(i64 x, i64 n) {
  i64 res = 1;
  i64 t = x;
  while (n > 0) {
    if (n & 1) res *= t;
    t *= t;
    n >>= 1;
  }
  return res;
}

void _main() {
  i64 n, m;
  cin >> n >> m;
  i64 a = n, b = 0;
  i64 ans = 0;
  for (i64 i = 40; i >= 0; i--) {
    i64 mxa = 0, mxb = b;
    if (m >> i & 1) {
      mxa = a;
    }
    i64 d = (mxa + mxb) / 2 * 2;
    {
      i64 c = min(d, mxb);
      ans += c << i;
      d -= c;
    }
    {
      i64 c = min(d, mxa);
      ans += c << i;
      d -= c;
      if (m >> i & 1) {
        i64 na = c, nb = b + (a - c);
        a = na, b = nb;
      }
    }
  }
  cout << ans << "\n";
}