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

int main() {
	string s;
	cin >> s;
	if(s.length()%2 != 0) {cout << "NO\n"; return 0;}
	vector<int> P(26,0);
	for(int i =0; i < s.length(); i++) P[s[i]-'a']++;
	sort(P.begin(),P.end());
	cout << ((P[25]*2 <= s.length())?"YES\n":"NO\n");
	return 0;}