#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
signed main(){
  string s;
  cin>>s;
  string t(s);
  sort(t.begin(),t.end());
  t.erase(unique(t.begin(),t.end()),t.end());
  cout<<(s.size()==t.size()?"YES":"NO")<<endl;
  return 0;
}