unordered_map<char, int> ladybug;
     int flag = 0;
     //counting frequency of character
     for(int i = 0; i< b.size(); i++){
        ladybug[b[i]]++;
     }
     
     //checking the count of the character greater than 1
     if(ladybug.size() > 1){
        for(int i = 0; i< ladybug.size(); i++){
            char c = i+ 65;
            if(ladybug[c]== 1 && c != '_') return "NO";
        }
     }
     
     //checking if any possible chance to switch 
     for(auto i : ladybug){
        if(i.first == '_'){flag = 1; break;}
     }
     
     // checking it is sorted or not if there is no chance to switch
     if(flag == 0){
        for(int i = 0; i< b.size();i++){
            if(b[i] == b[i+1] || b[i] == b[i-1]){
                flag = 1;
            }else{
                flag = 0;
                break;
            }
        }
     }
     
     return  flag == 0 ? "NO" : "YES";