#include "bits/stdc++.h" using namespace std; #define fastcin {\ cin.tie(0);\ ios::sync_with_stdio(false);\ } #define rep(i, a, b) for(int i = a; i < b; i++) #define rrep(i, a, b) for(int i = a; i > b; i--) #define fore(i, a) for(auto &i:a) #define print(x) cout << x << "\n" #define SORT(a, n) sort(a, a+n); #define REVERSE(a,n) reverse(a,a+n); #define VSORT(v) sort(v.begin(), v.end()); #define VREVERSE(v) reverse(v.begin(), v.end()); #define MOD 1000000007 typedef long long ll; int main() { fastcin; string S; cin >> S; map m; int count; rep(i, 0, 13) { m[S[i]]++; int tmp = m[S[i]]; if(tmp==1) count++; else if(tmp > 2) { cout << "Impossible" << endl; return 0; } } if(count!=7) { cout << "Impossible" << endl; return 0; } fore(x, m) { if(x.second==1) { cout << x.first << endl; return 0; } } }