#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  string s;
  cin >> s;
  long long int i, j;
  string s1 = "Danil", s2 = "Olya", s3 = "Slava", s4 = "Ann", s5 = "Nikita";
  map<string, long long int> mp;
  map<string, long long int>::iterator it;
  for (i = 0; i < s.size(); i++) {
    if (s[i] == 'D') {
      j = 0;
      while (s[i] == s1[j] && i < s.size()) {
        i++;
        j++;
        if (j == 5) {
          mp[s1]++;
          break;
        }
      }
      i--;
    } else if (s[i] == 'O') {
      j = 0;
      while (s[i] == s2[j] && i < s.size()) {
        i++;
        j++;
        if (j == 4) {
          mp[s2]++;
          break;
        }
      }
      i--;
    } else if (s[i] == 'S') {
      j = 0;
      while (s[i] == s3[j] && i < s.size()) {
        i++;
        j++;
        if (j == 5) {
          mp[s3]++;
          break;
        }
      }
      i--;
    }
    if (s[i] == 'A') {
      j = 0;
      while (s[i] == s4[j] && i < s.size()) {
        i++;
        j++;
        if (j == 3) {
          mp[s4]++;
          break;
        }
      }
      i--;
    }
    if (s[i] == 'N') {
      j = 0;
      while (s[i] == s5[j] && i < s.size()) {
        i++;
        j++;
        if (j == 6) {
          mp[s5]++;
          break;
        }
      }
      i--;
    }
  }
  if (mp.size() > 1 || mp.size() == 0)
    cout << "NO"
         << "\n";
  else if (mp.size() == 1) {
    it = mp.begin();
    if (it->second == 1)
      cout << "YES"
           << "\n";
    else
      cout << "NO"
           << "\n";
  }
  return 0;
}
