import java.util.*;

public class Main {

    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int[] c = new int[26];
        for (int i=0;i<s.length();i++)c[s.charAt(i)-'A']++;
        boolean b = true;
        for (int i=0;i<26;i++)if (c[i]!=0&&c[i]!=2)b=false;
        if (b)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