#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

int cnt[26];
string S;

int main() {
  cin >> S;
  for (int i = 0; i < S.size(); i++) {
    cnt[S[i] - 'A']++;
  }
  for (int i = 0; i < 26; i++) {
    if (cnt[i] > 1) {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}