import java.util.*;
public class Solution {
    //Insert one char from stringstream
    HashMap<Character,Integer> map=new LinkedHashMap<Character,Integer>();
    public void Insert(char ch)
    {
        if(map.containsKey(ch)){
            map.put(ch,map.get(ch)+1);
        }else{
            map.put(ch,1);
        }
        
    }
  //return the first appearence once char in current stringstream
    public char FirstAppearingOnce()
    {
        for(Character c:map.keySet()){
            if(map.get(c)==1){
                return c;
            }
        }
        return '#';
    }
}