#include <bits/stdc++.h>
using namespace std;
int main(){
  string s; cin >> s;
  map<char, int> m;
  for (int i = 0; i < (int) s.size(); i++) {
    m[s[i]]++;
  }
  for (auto it = m.begin(); it != m.end(); it++) {
    if (it -> second > 1) {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}