import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
      	String s= sc.next();
      	String t=sc.next();
      	int ans=0;
      	for (int i = 0; i < s.length(); i++) {
			if((s.charAt(i))!=(t.charAt(i))){ans++;}
		}
      	System.out.println(""+(ans));
}
}
/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