#include <bits/stdc++.h>
using namespace std;
int main() {
  string a, b[5] = {"Danil", "Olya", "Slava", "Ann", "Nikita"}, c;
  cin >> a;
  int cnt = 0;
  for (int i = 0; i < 5; i++) {
    size_t f = a.find(b[i]);
    if (f != string::npos) {
      cnt++;
      c = a.substr(f + b[i].size());
      size_t k = c.find(b[i]);
      if (k != string::npos) {
        cout << "NO" << endl;
        return 0;
      }
    }
  }
  if (cnt == 1)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
