#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for (int i=0;i<(int)(n);i++)

int main(){
  string x,y;
  cin>>x>>y;
  vector<int> ans;
  while(x.size()>0&&y.size()>0){
    if(x.back()==y.back()){
      ans.push_back(0);
    }else{
      ans.push_back(1);
    }
    x.pop_back();
    y.pop_back();
  }
  while(x.size()>0){ ans.push_back(x.back()-'0'); x.pop_back();}
  while(y.size()>0){ ans.push_back(y.back()-'0'); y.pop_back();}
  ll c=0;
  ll pw=1;
  for(int i:ans){
    c+=i*pw;
    pw*=2;
  }
  cout<<c<<endl;
}