import core.bitop;
import std.algorithm;
import std.array;
import std.ascii;
import std.container;
import std.conv;
import std.format;
import std.math;
import std.random;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

void main()
{
  string s = readln.chomp;
  int[char] cnt;
  foreach (c; s) {
    cnt[c]++;
  }
  int two = 0;
  int one = 0;
  char trg;
  foreach (k, v; cnt) {
    switch (v) {
      case 1:
      ++one;
      trg = k;
      break;
      case 2:
      ++two;
      default:
    }
  }
  bool yes = cnt.keys.length == 7 && two == 6 && one == 1;
  if (yes) {
    writeln = trg;
  } else {
    writeln = "Impossible";
  }
}