#include<bits/stdc++.h>
using namespace std;

int main() {
	int i,a;
	string A,B,S;
	cin >> S;
	sort(S.begin(),S.end());
	A = "abcdefghijklm";
	if(A==S){
		cout << A << endl;
	}
	else if(A!=S){
		for(i=0;A[i]==S[i];i++)
			if(A[i+1]==S[i]){
				for(i=i+1;A[i+1]==S[i];i++)
			
				if((A[i]==S[i])) {
					B=A[i];
					for(a=i;A[a]==S[a];a++);
					}}
			else if(A[i-1]==S[i]){
				B=A[i];
				for(a=i-1;A[a]==S[a+1];a++);
			
			if(A[a]==S[a]){
				for(a=i;A[a]==S[a];a++);
			}}
			}
			
		
	
	if(a==13) {cout << A[i] << endl;} else {cout << "Impossible" << endl;}
	
	return 0;
}