#include<stdio.h>

int main(void){
	int b[128]={0},i,k,n,x;
	char s[16];
	scanf("%s",s);
	for(i = 0;i < 13;i++){b[s[i]]++;}
	for(i = 97;i <= 109;i++){
		if(b[i] >= 1){k++;}else{n = i;}
	}
	if(k == 13){printf("a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm\n");}
	if(k == 12){printf("%c\n",n);}
	if(k <= 11){printf("Impossible\n");}
	return 0;
}