#include <bits/stdc++.h>
using namespace std;
int main() {
  string str, Danil = "Danil", Olya = "Olya", Slava = "Slava", Ann = "Ann",
              Nikita = "Nikita";
  cin >> str;
  int i, d = 0, o = 0, s = 0, a = 0, n = 0, count = 0;
  for (i = 0; i < str.size(); i++) {
    if (str[i] == Danil[d]) {
      d++;
      if (d == Danil.size()) count++;
      o = 0, s = 0, a = 0, n = 0;
    } else if (str[i] == Olya[o]) {
      o++;
      if (o == Olya.size()) count++;
      d = 0, s = 0, a = 0, n = 0;
    } else if (str[i] == Slava[s]) {
      s++;
      if (s == Slava.size()) count++;
      o = 0, d = 0, a = 0, n = 0;
    } else if (str[i] == Ann[a]) {
      a++;
      if (a == Ann.size()) count++;
      o = 0, s = 0, d = 0, n = 0;
    } else if (str[i] == Nikita[n]) {
      n++;
      if (n == Nikita.size()) count++;
      o = 0, s = 0, a = 0, d = 0;
    } else {
      d = 0, o = 0, s = 0, a = 0, n = 0;
      if (str[i] == Danil[0]) i--;
      if (str[i] == Olya[0]) i--;
      if (str[i] == Slava[0]) i--;
      if (str[i] == Ann[0]) i--;
      if (str[i] == Nikita[0]) i--;
    }
  }
  if (count == 1)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
  return 0;
}
