7.2.10

import java.util.Scanner;
public class Main {


    static char  doubleChar(String a)
    {
        for(int i=0,Length=a.length();i<Length;i++)
        {
            for(int j=i+1;j<Length;j++)
            {
                if (a.charAt(i)==a.charAt(j) && a.charAt(i)!=' ') return a.charAt(i);
            }
        }
        return '0';
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String a=in.nextLine();
        System.out.print(doubleChar(a));
    }
}