import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scr =new Scanner(System.in);
	
		String in = scr.next();
		String out = scr.next();
		
		String a = out.substring(0,out.length()-1);
	
		if(in.equals(a)&&in.length() != out.length()) {
			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