#include <bits/stdc++.h>
using namespace std;
int NrAp(char s[], char t[]) {
  int ct = 0, nt = strlen(t);
  char *p = strstr(s, t);
  while (p) {
    ct++;
    p = strstr(p + nt, t);
  }
  return ct;
}
int main() {
  char s[105];
  cin.getline(s, 105);
  if (NrAp(s, "Danil") + NrAp(s, "Olya") + NrAp(s, "Slava") + NrAp(s, "Ann") +
          NrAp(s, "Nikita") ==
      1)
    cout << "YES";
  else
    cout << "NO";
  return 0;
}
