class Solution

 {

 public:

   //Insert one char from stringstream

     void Insert(char ch)

     {

         s = s + ch;

         if(cha[ch])

             cha[ch]++;

         else

             cha[ch] = ;

     }

   //return the first appearence once char in current stringstream

     char FirstAppearingOnce()

     {

         int length = s.size();

         for(int i=; i<length; i++){

             if(cha[s[i]] == )

                 return s[i];

         }

         return '#';

     }

 private:

     char cha[]={};

     string s;

 };