#include<iostream>
#include<vector>
#include<string>
#include<algorithm>	
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<stack>
#include<cstdio>
#include<sstream>
#include<iomanip>
#include<assert.h>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mt make_tuple
#define all(in) in.begin(),in.end()
#define shosu(x) fixed<<setprecision(x)
using namespace std;
//kaewasuretyuui
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<vp> vvp;
typedef vector<string> vs;
typedef vector<double> vd;
typedef tuple<int,int,int> tp;
typedef vector<tp> vt;
typedef vector<vd> vvd;
typedef pair<int,pii> pip;
typedef vector<pip>vip;
const double PI=acos(-1);
const double EPS=1e-7;
const int inf=1e8;
const ll INF=1e16;
int dx[]={0,1,0,-1};
int dy[]={1,0,-1,0};
int main(){
	string s;
	map<string,int>ma;
	ma["aabcdefghijklm"]=1;
	ma["abbcdefghijklm"]=1;
	ma["abccdefghijklm"]=1;
	ma["abcddefghijklm"]=1;
	ma["abcdeefghijklm"]=1;
	ma["abcdeffghijklm"]=1;
	ma["abcdefgghijklm"]=1;
	ma["abcdefghhijklm"]=1;
	ma["abcdefghiijklm"]=1;
	ma["abcdefghijjklm"]=1;
	ma["abcdefghijkklm"]=1;
	ma["abcdefghijkllm"]=1;
	ma["abcdefghijklmm"]=1;
	cin>>s;
	int co=0;
	for(char c='a';c!='n';c++){
		string t=s+c;
		sort(all(t));
		if(ma[t]){
			cout<<c<<endl;
			co++;
		}
	}
	if(!co)cout<<"Impossible"<<endl;
}