#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(void){
  string S;
  cin >> S;
  vector<int> panel(26, 0);
  for(int i = 0; i < (int)S.size(); i++){
    int idx = S[i] - 'A';
    if(0 != panel[idx]){
      cout << "NO" << endl;
      return 0;

    }
    panel[idx]++;

  }
  cout << "YES" << endl;
  return 0;

}