#include <bits/stdc++.h>
using namespace std;
string name[5] = {"Danil", "Olya", "Slava", "Ann", "Nikita"};
string s;
int cnt = 0;
int main() {
  cin >> s;
  for (int j = 0; j < 5; j++) {
    while (s.find(name[j]) != string::npos) {
      cnt++;
      s[s.find(name[j])] = '*';
    }
  }
  if (cnt == 1)
    cout << "YES";
  else
    cout << "NO";
}
