#include <iostream>

int main()
{
    char in[14];
    int count[13] = {0};
    int twocount = 0;
    
    std::cin >> in;
    
    for(int i = 0; i < 13; i++)
    {
        count[in[i] - 'a']++;
        
        
        if(count[in[i] - 'a'] == 2)
        {
            twocount++;
        }
        if((count[in[i] - 'a'] >= 3) || (twocount >= 2))
        {
            std::cout << "Impossible" << std::endl;
            return 0;
        }
    }
    
    if(twocount == 0)
    {
        std::cout << "a\nb\bc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm" << std::endl;
    }
    else
    {
        for(int i = 0; i < 13; i++)
        {
            if(count[in[i] - 'a'] == 0)
            {
                std::cout << (char)(i + 'a') << std::endl;
            }
        }
    }
    
    return 0;
}