#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
  string S;
  cin>>S;
  set<char> s;
  for(int i=0;i<S.size();i++) s.insert(S[i]);
  if(s.size() == S.size()) cout<<"YES"<<endl;
  else cout<<"NO"<<endl;
}