import java.util.LinkedHashMap;
import java.util.Map;

public class Test {
    public static void main(String[] args) {

        String s = "swiss";
        LinkedHashMap<Character,Integer> hm = new LinkedHashMap<>();
        for(int i=0;i<s.length();i++) {
            hm.put(s.charAt(i), hm.getOrDefault(s.charAt(i), 0)+1);
        }
        for(Map.Entry<Character, Integer> e : hm.entrySet()) {
            if(e.getValue() == 1) {
                System.out.println(e.getKey());
                break;
            }           
        }
    }
}