import java.util.*;

public class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        Map<Character, Integer> map = new HashMap<>();
        for (char c : s.toCharArray()) {
            int count = map.getOrDefault(c, 0);
            map.put(c, ++count);
        }
        Set<Character> cs = map.keySet();
        if (cs.size() != 2) {
            System.out.println("No");
            return;
        }
        for (int i : map.values()) {
            if (i != 2) {
                System.out.println("No");
                return;
            }
        }

        System.out.println("Yes");
    }
}
/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