# include # include # include # include # include # include # include # include # include # include # include # include # include # include # include # include # include using namespace std; using LL = long long; using ULL = unsigned long long; constexpr int MOD = 1000000000 + 7; constexpr int INF = 2000000000; constexpr int HINF = INF / 2; constexpr double DINF = 100000000000000000.0; constexpr long long LINF = 9223372036854775807; constexpr long long HLINF = 4500000000000000000; const double PI = acos(-1); int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 }; #define ALL(x) (x).begin(),(x).end() #define mp make_pair #define eb emplace_back int C[30]; int main(){ string s; cin >> s; for (int i = 0; i < s.size(); i++) { C[s[i] - 'a']++; } int a = 0; for (int i = 0; i < 30; i++) { if (C[i] == 1)a++; } if (a != 1) { cout << "Impossible" << endl; return 0; } for (int i = 0; i < 30; i++) { if (C[i] == 1) { cout << char(i + 'a') << endl; return 0; } } }