#include<iostream>
#include<algorithm>
#include<cmath>
using namespace std;
int main() {
  int a[26]={0};
  string s;
  cin >> s;
  for(int i=0; i<s.size(); i++) {
      if(a[s[i]-'A']==0) {
          a[s[i]-'A']++;
      }
      else {
          cout << "NO" << endl;
          return 0;
      }
  }
  cout << "YES" << endl;
}