#include <bits/stdc++.h>
using namespace std;

signed main() {
  ios::sync_with_stdio(false);
  string S;
  cin >> S;
  map<int, int> mp;
  for (int i = 0; i < S.size(); ++i) ++mp[S[i]];
  for (auto it = mp.begin(); it != mp.end(); ++it)
    if (it->second > 1) cout << "NO" << endl, exit(0);
  cout << "YES" << endl;

}