import java.util.Scanner;


public class Main {
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        char[] ca = str.toCharArray();
        int[] count = new int[4];
        for (int i =0; i < ca.length; i++) {
            for (char c : ca) {
                if (c == ca[i]) {
                    count[i]++;
                }
            }
        }
        boolean key = true;
        for (int c:count) {
            if (c != 2) {
                key = false;
            }
        }
        if (key) {
            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