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

int main(){
  string s  ;
  cin >> s;
  vector<int> tmp ={};
  for(int i=0;i<s.length();i++){
    for(int x : tmp) {
      if(x == s[i]){
        cout << "NO" << endl;
        return 0;
      }
    }
    tmp.push_back(s[i]);
  }
  cout << "YES" << endl;
  return 0;
}