import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		Scanner scanner = new Scanner(System.in);
		String input = scanner.nextLine();
		
		String trimed = input.replace(input.substring(0, 1), "");
		if(trimed.length()==2){
			if(trimed.charAt(0) == trimed.charAt(1)){
				System.out.println("Yes");
			} else {
				System.out.println("No");
			}
		} 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