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

int a[10];

int main(){
  map<char,int>mp;
  string s;
  cin >> s;
  for(int i=0;i<s.length();i++){
    mp[s.at(i)]++;
  }
  for(auto e:mp){
    if(e.second>1){
      cout<<"NO"<<endl;
      return 0;
    }
  }
  cout<<"YES"<<endl;
  return 0;
}