import java.util.*;
public class Main{
  public static void main(String[] args)
  {
    Scanner sc=new Scanner(System.in);
   String s1=sc.next();
   String s2=sc.next();
  int c=0;
  if(!(s1.equals(s2)))
  {
   for(int i=0;i<s1.length();i++) 
  {
       if(s1.charAt(i)!=s2.charAt(i))
	c++;
   }
  }
   System.out.println(c); 
  }
   
}
/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