#include <iostream>
#include <vector>
#include <algorithm>
#include <map>

using namespace std;


int main() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);

  unsigned long long A, C;
  cin >> A >> C;
  unsigned long long B = A ^ C;
  cout << B << endl;
  return 0;
}