string isValid(string s) {
    bool valid = true;
    map<char,int> ocurrence;
    for(int i = 0;i<s.size();i++) ocurrence[s[i]]++;
    map<int,int> repeatence;
    map<char,int>::iterator itr;
    for(itr = ocurrence.begin();itr!=ocurrence.end();++itr)
        repeatence[itr->second]++;
    
    /* debug
    cout << "repeatence: " << repeatence.size()<< endl;
    for(auto i:repeatence)
        cout << " " << i.first << " " << i.second << endl;
    
    */
    
    
    if(repeatence.size()>2) valid = false;
    if(repeatence.size()==2) {
        
        /* debug
        
        
        map<int,int>:: iterator it;
        it = repeatence.begin();
        cout << "repeatence.begin()->first: " << it->first << endl;
        ++it;
        cout << "repeatence.end()->first: " << it->first << endl;
        
        cout << "abs(repeatence.begin()->first - repeatence.end()->first): "
            << abs(repeatence.begin()->first - repeatence.end()->first) << endl;
            
        
        */
        
        map<int,int>:: iterator it;
        it = repeatence.begin();
        int diff = it->first;
        int val[2];
        val[0] = it->second;
        if(diff == 1 and val[0] == 1) goto xx;
        ++it;
        diff -= it->first;
        val[1] = it->second;
        diff=abs(diff) - 1;
        if(diff) valid = false;
        
        //cout << valid << endl;
        
        if(!(val[0] == 1 || val[1] == 1))
            valid = false;
            
    } 
    xx:
    
    return valid?"YES":"NO";
}