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

int main() {
  string S;
  cin >> S;
  vector<int> a(26);

  for (char c : S)
    a.at(c - 'A')++;

  for (int b : a) {
    if (b > 1) {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
}