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

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int a, b;
  cin >> a >> b;
  int ans = 0, two = 1;
  while (a || b) {
    if (!(a % 10 == b % 10)) {
      ans += two;
    }
    a /= 10;
    b /= 10;
    two *= 2;
  }
  cout << ans << endl;
  return 0;
}