#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("avx")
using namespace std;
template <typename T1, typename T2>
ostream& operator<<(ostream& o, const pair<T1, T2> p) {
  o << "(" << p.first << ":" << p.second << ")";
  return o;
}
template <typename iterator>
inline size_t argmin(iterator begin, iterator end) {
  return distance(begin, min_element(begin, end));
}
template <typename iterator>
inline size_t argmax(iterator begin, iterator end) {
  return distance(begin, max_element(begin, end));
}
template <typename T>
T& maxset(T& to, const T& val) {
  return to = max(to, val);
}
template <typename T>
T& minset(T& to, const T& val) {
  return to = min(to, val);
}
void bye(string s, int code = 0) {
  cout << s << endl;
  exit(0);
}
mt19937_64 randdev(8901016);
inline long long int rand_range(long long int l, long long int h) {
  return uniform_int_distribution<long long int>(l, h)(randdev);
}
namespace {
class MaiScanner {
 public:
  template <typename T>
  void input_integer(T& var) {
    var = 0;
    T sign = 1;
    int cc = getchar_unlocked();
    for (; cc < '0' || '9' < cc; cc = getchar_unlocked())
      if (cc == '-') sign = -1;
    for (; '0' <= cc && cc <= '9'; cc = getchar_unlocked())
      var = (var << 3) + (var << 1) + cc - '0';
    var = var * sign;
  }
  inline int c() { return getchar_unlocked(); }
  inline MaiScanner& operator>>(int& var) {
    input_integer<int>(var);
    return *this;
  }
  inline MaiScanner& operator>>(long long& var) {
    input_integer<long long>(var);
    return *this;
  }
  inline MaiScanner& operator>>(string& var) {
    int cc = getchar_unlocked();
    for (; !(0x21 <= (cc) && (cc) <= 0x7E); cc = getchar_unlocked())
      ;
    for (; (0x21 <= (cc) && (cc) <= 0x7E); cc = getchar_unlocked())
      var.push_back(cc);
    return *this;
  }
  template <typename IT>
  void in(IT begin, IT end) {
    for (auto it = begin; it != end; ++it) *this >> *it;
  }
};
}  // namespace
MaiScanner scanner;
long long int m, n, kei;
int cnt[26];
int main() {
  string str;
  scanner >> str;
  n = str.size();
  for (auto i = 0ll; (i) < (n); ++(i)) {
    cnt[str[i] - 'a']++;
  }
  sort(cnt, cnt + 26);
  int sum = 0;
  for (auto i = 0ll; (i) < (25); ++(i)) sum += cnt[i];
  if (sum + 1 < cnt[25] * 2) bye("NO");
  bye("YES");
  return 0;
}
