import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        char[] lis = new char[256];

        for (int i = 0; i < 4; ++i) {
            lis[s.charAt(i)] += 1;
        }
        for (int i = 0; i < 256; ++i) {
            if (lis[i] != 0 && lis[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