// yukicoder: No.548 国士無双
// 2019.4.20 bal4u

#include <stdio.h>

char f[128];
char s[15], *p = s;

int main()
{
	int c, max = 0;
	scanf("%s", s);
	while (*p) {
		c = *p++;
		if (++f[c] > max) max = f[c];
	}
	if (max > 2) puts("Impossible");
	else if (max == 2) {
		for (c = 'a'; c <= 'm'; c++) if (f[c] == 0) {
			putchar(c), putchar('\n'); break;
		}
	} else puts("a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm");
	return 0;
}