public static string happyLadybugs(string b)
    {
        Dictionary<char, int> d = new Dictionary<char, int>();
        foreach(char c in b)
        {
            if(!d.ContainsKey(c))
            {
                d.Add(c, 0);
            }
            d[c]++;
        }
        bool has_ = false;
        foreach(var item in d)
        {
            if(item.Key != '_' && item.Value == 1)
            {
                return "NO";
            }
            if(item.Key == '_')
            {
                has_ = true;
            }
        }
        
        if(!has_)
        {
            for(int i = 0; i < b.Count() - 1; i++)
            {
                if(b[i] != b[i+1] && (i != 0 && b[i] != b[i-1]))
                {
                    return "NO";
                }
            }
        }
        
        return "YES";
    }