#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)

int main() {
  string s;
  cin>>s;
  vector<int> freq(26);
  for(char& ch : s) {
    freq[static_cast<int>(ch-'a')]++;
  }
  rep(i,26) {
    if(freq[i]>1) {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}