#include<string>
#include<deque>
#include<queue>
#include<vector>
#include<algorithm>
#include<iostream>
#include<set>
#include<cmath>
#include<tuple>
#include<chrono>
#include<functional>
#include<iterator>
//#include<random>
#include<unordered_set>
#include<map>
using namespace std;
typedef long long int llint;
#define mp make_pair
#define mt make_tuple
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define fir first
#define sec second
#define res resize
#define ins insert
#define era erase
const int mod=1000000007;
const int big=1e8+10;
const long double pai=3.141592653589793238462643383279;
template <class T,class U>void mineq(T& a,U b){if(a>b){a=b;}}
template <class T,class U>void maxeq(T& a,U b){if(a<b){a=b;}}
int gcd(int a,int b){if(a%b==0){return b;}else return gcd(b,a%b);}//a>b
int main(void){
	string str;cin>>str;
	sort(str.begin(),str.end());
	char ans='z';
	if(str=="abcdefghijklm"){
		for(char c='a';c!='n';c++){cout<<c<<endl;}return 0;
	}
	char c;
	for(c='a';c!='n';c++){
		auto it=find(str.begin(),str.end(),c);
		if(it==str.end()){
			if(ans!='z'){cout<<"Impossible"<<endl;return 0;}
			ans=c;
		}
	}
	cout<<ans<<endl;
	return 0;
}