#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

int main(){
  string S; cin >> S;
  sort(S.begin(), S.end());
  for(int i = 1; i < (int)S.size(); i++){
    if(S[i-1] == S[i]){
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
}