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

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String str = sc.next();
    boolean ret = true;
    Map<Character, Integer> map = new HashMap<Character, Integer>();
    for (char c: str.toCharArray())
      if (map.containsKey(c))
        map.put(c, map.get(c) + 1);
      else
        map.put(c, 1);
    for (Map.Entry<Character, Integer> entry : map.entrySet()) {
      if (entry.getValue() != 2)
        ret = false;
    }
    if (ret)
      System.out.print("Yes");
    else
      System.out.print("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