#include<iostream>
#include<vector>
#include<string>
#include<sstream>


using namespace std;


int firstNonRepeating(vector<unsigned int> &arr, int & n)
{

    for (int i = 0; i < n; i++) {
        int j;
        for (j = 0; j < n; j++)
            if (i != j && arr[i] == arr[j])
                break;
        if (j == n)
            return arr[i];
    }
    return -1;
}
void Dec2Hex(int no)
{
    int hex=0;
    if(!no)
        return;
    else {
        hex=no%16;
        Dec2Hex(no/16);
    }
    if(hex>9)
        printf("%c",'a'+(hex-10));
    else
        printf("%d",hex);


}



int main(){

    cin.sync_with_stdio(false);
    cout.sync_with_stdio(false);
string Input;

// while (Input != ".")
//  {
//      cin >> Input;
//          if (Input == ".")
//               break;

//  }
getline(cin, Input, '.');
vector<unsigned int> dna;

for (unsigned int i = 0; i < Input.length(); i += 5)
{
    stringstream stream(Input.substr(i, 5));
    unsigned int num;
    while (stream >> hex >> num)
    {
        dna.push_back(num);
    }

}


int size = dna.size();

  Dec2Hex(firstNonRepeating(dna, size));

return 0;
}