#include<bits/stdc++.h>
using namespace std;
int d[256];
int main(){
string s ;cin >> s;
for(int i = 0 ; i < s.size() ; i++){
d[s[i]]++;
}
int _max = 0 ;
for(int i = 0 ; i < s.size() ; i++){
_max = max(_max,d[s[i]]);
}
if(_max <= ((int)s.size()-1)/2 + 1){
cout << "YES";
}
else cout << "NO";
}
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