#include <bits/stdc++.h>
using namespace std;

string s;
bool sub(char c) {
  bool odd = false;
  bool even = false;
  if (s.back() == c) return false;
  for (int i = 0; i < s.size(); ++i) {
    if (s[i] == c) {
      (i % 2 == 0 ? even : odd) = true;
    }
  }
  return odd ^ even;
}

int main() {
  getline(cin, s);
  bool ok = false;
  for (char c = 'a'; c <= 'z'; ++c) {
    ok |= sub(c);
  }
  cout << (ok ? "Yes" : "NO") << endl;
}