#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ul;
typedef signed long long ll;
ul over = 1000000007;

mt19937 mt(time(nullptr));
// uniform_int_distribution< int > rand_int(0, 10) // rand[0, 10] inclusive

int main(void)
{
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed;
  string s;
  cin >> s;
  vector< bool > flg(26, true);
  for (ul i=0; i<s.size(); ++i) {
    ul idx = s[i]-'A';
    if (!flg[idx]) {
      cout << "NO" << endl;
      return 0;
    }
    flg[idx] = false;
  }
  cout << "YES" << endl;
  return 0;
}