import java.util.*;
import java.lang.*;
import java.io.*;



/* Name of the class has to be "Main" only if the class is public. */



public class Main
{
     
     
     static int mod(int a, int m) 
{ 
    return (a%m + m) % m; 
}
   
    
public static void main (String[] args) throws java.lang.Exception
{Scanner scn = new Scanner(System.in) ;

String s  = scn.nextLine() ;
String t  = scn.nextLine() ; int count  = 0 ;

for(int i = 0 ; i <  s.length() ; i++ )
{
    if(s.charAt(i) != t.charAt(i) )count++ ;
    
    
    
}

System.out.println(count) ;
              
}
}




              
             
/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