c[999];s;t;main(i){for(;i++<14;)c[getchar()]++?s++:0;for(;--i>1;)c[i+95]||(t=i+95);printf(s>1?"Impossible":s?"%c":"a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm",t);}