#include <bits/stdc++.h>
#define int long long
using namespace std;
const int MOD = 1000000007;

signed main() {
  string S;
  cin >> S;
  
  set<char> A;
  for( int i = 0; i < S.size(); i++ ){
    if( A.count(S.at(i)) ){
      cout << "NO" << endl;
      return 0;
    }else A.insert(S.at(i));
  }
  
  cout << "YES" << endl;
}