/* author: kyawa */
#include<bits/stdc++.h>
using namespace std;

/*
 考察
 
 */

int main(){
    string A, B; cin >> A >> B;
    reverse(A.begin(), A.end());
    reverse(B.begin(), B.end());
    A.resize(60, '0');
    B.resize(60, '0');
    int64_t res = 0;
    for(int64_t i = 0; i < 60; i++){
        res += (1<<i) * ((A[i] - '0')^(B[i] - '0'));
    }
    cout << res << '\n';
}