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

using ll = long long;
#define rep(i, n) for (int i = 0; i < n; i++)
#define INF (1LL << 60)
#define all(v) (v).begin(), (v).end()

template <class T>
void chmin(T &a, T b) {
    if (a > b) a = b;
}

template <class T>
void chmax(T &a, T b) {
    if (a < b) a = b;
}

int main() {
    string A, B;
    cin >> A >> B;
    ll N = max(A.length(), B.length());
    while (A.size() < N) A = '0' + A;
    while (B.size() < N) B = '0' + B;
    ll ans = 0, b = 1;
    rep(i, N) {
        if (A[N - i - 1] != B[N - i - 1]) {
            ans += b;
        }
        b *= 2;
    }
    cout << ans << endl;
}