#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <iomanip>
#include <random>
#include <cassert>
#include <cstring>
using namespace std;

#define GET_ARG(a,b,c,F,...) F
#define REP3(i,s,e) for (i = s; i <= e; i++)
#define REP2(i,n) REP3 (i,0,(int)(n)-1)
#define REP(...) GET_ARG (__VA_ARGS__,REP3,REP2) (__VA_ARGS__)
#define RREP3(i,s,e) for (i = s; i >= e; i--)
#define RREP2(i,n) RREP3 (i,(int)(n)-1,0)
#define RREP(...) GET_ARG (__VA_ARGS__,RREP3,RREP2) (__VA_ARGS__)
#define DEBUG(x) cerr << #x ": " << x << endl

int main(void) {
    string s;
    cin >> s;
    string t = "abcdefghijklm";
    int cnt = 0;
    for (auto c: t) {
        if (s.find(c) == string::npos) {
            cnt++;
        }
    }
    if (cnt > 1) {
        puts("Impossible");
        return 0;
    }
    else {
        for (auto c: t) {
            if (cnt == 0 || s.find(c) == string::npos) {
                printf("%c\n",c);
            }
        }
    }
    return 0;
}