text: #include <bits/stdc++.h>
  using namespace std;
  int main()
  {
      string s;
      cin >> s;
      set<char> se;
      for (int i = 0; i < (int)s.size(); i++)
      {
          se.insert(s.at(i));
      }
      cout << ((int)s.size() == (int)se.size() ? "yes" : "no") << endl;
  }
  