#include <iostream>
using namespace std;

string encrypt(string s, string key)
{
    string ans = "";
    key += s;
    for(int i=0; i<s.length(); i++) {
        ans += (char)('A' + (s[i]-'A' + key[i] - 'A')%26);
    }
    return ans;

}

string decrypt(string s, string key)
{
    string ans = "";
    for(int i=0; i<s.length(); i++) {
        char ch = (char)('A' + (s[i] - key[i] + 26)%26);
        ans += ch;
        key += ch;
    }
    return ans;

}
int main()
{
    string s, key;

    cin >> s >> key;
//    cout << encrypt(s, key) << endl;
    cout << decrypt(s, key) << endl;
}