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

#define REP(i, a, b) for (int i = int(a); i < int(b); i++)
#define dump(s) cerr << __LINE__ << "\t:" << #s << " = " << (s) << endl
    
using namespace std;

int main () {
    unsigned long long int A, C;
    cin >> A >> C;
    cout << (A ^ C) << endl;
    return 0; 
}