#include <iostream>
#include <string>
using namespace std;
int main()
{
    int N = 6;
    //cin >> N;
    //char s[] = "ACDBCB";
    //char s[6] = {'A', 'C', 'D', 'B', 'C', 'B'};
    //string s = "ACDBCB";
    string s;
    cin >> s;

    int a = 0;
    int b = N - 1;
    while(a <= b)
    {
        bool left = false;
        for(int i = 0; a + i <= b; ++i)
        {
            if(s[a + i] < s[b - i])
            {
                left = true;
                break;
            }else if(s[a + i] > s[b - i])
            {
                left = false;
                break;
            }
        }
        if(left)
        {
            cout << s[a++];
        }else
        {
            cout << s[b--];
        }
    }
    cout << endl;
    return 0;
}