/* -*- coding: utf-8 -*- * * 587.cc: No.587 七対子 - yukicoder */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; /* constant */ /* typedef */ /* global variables */ int cs[26]; /* subroutines */ /* main */ int main() { string s; cin >> s; for (int i = 0; i < 13; i++) cs[s[i] - 'a']++; int on = 0, tn = 0, oc = 0; for (int i = 0; i < 26; i++) { if (cs[i] == 1) on++, oc = i; else if (cs[i] == 2) tn++; } if (on == 1 && tn == 6) printf("%c\n", oc + 'a'); else puts("Impossible"); return 0; }