import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        char[] s = sc.next().toCharArray();
        Map<Character, Integer> map = new HashMap<>();
        for (int i = 0; i < s.length; i++) {
            if(!map.containsKey(s[i])) {
                map.put(s[i], 1);
            }
            else {
                map.put(s[i], map.get(s[i]) + 1);
            }
        }
        if(map.size() == 2 && map.get(s[0]) == 2) {
            System.out.println("Yes");
        }
        else {
            System.out.println("No");
        }
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz