import std.algorithm, std.conv, std.range, std.stdio, std.string;

void main()
{
  auto s = readln.chomp;
  auto t = new int[](26);
  foreach (c; s) t[c-'a']++;

  auto i1 = t.count(1);
  auto i2 = t.count(2);

  if (i1 == 1 && i2 == 6) {
    writeln(cast(char)(t.countUntil(1)+'a'));
  } else {
    writeln("Impossible");
  }
}