#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a;i < n;i++)
using namespace std;

int main() {
    int s, f;
    rep(i, 0, 13) {
        s |= 1 << (getchar() - 'a');
    }
    rep(i, 0, 13) {
        if ((s | 1 << i) == 0x1FFF) {
            printf("%c\n", 'a' + i);
            f++;
        }
    }
    if (f == 0)puts("Impossible");
}