#include <bits/stdc++.h>
using namespace std;
const int INF = 10000000;
const int MAX = 150;
string s;
int found(string aux) {
  int ans = 0;
  int cnt = 0;
  for (int i = 0; i < s.size(); i++) {
    for (int j = 0, k = i; j < aux.size(); j++, k++) {
      if (k == s.size()) break;
      if (aux[j] == s[k])
        cnt++;
      else {
        cnt = 0;
        break;
      }
    }
    if (cnt == aux.size()) ans++;
  }
  return ans;
}
int main() {
  cin >> s;
  int ans = 0;
  ans += found("Danil");
  ans += found("Olya");
  ans += found("Slava");
  ans += found("Ann");
  ans += found("Nikita");
  if (ans == 1)
    puts("YES");
  else
    puts("NO");
  return 0;
}
