import java.util.Scanner;

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

		int i;
		int length = s.length();
		int[] sum = new int[10000];
		for(i = 0; i < length; i++) {
			sum[s.codePointAt(i)]++;
		}
		for(i = 0; i < length; i++) {
			if(sum[s.codePointAt(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