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

int main(){
  std::vector<int> v(26,0);
  string s;
  cin>>s;
  int out=0;
  for(int i=0;i<s.size();i++){
    v[(int)s[i]-65]++;
    if(v[(int)s[i]-65]>=2)out++;
  }
  if(out)cout<<"NO"<<endl;
  else cout<<"YES"<<endl;
}