import java.util.*;
import java.io.*;
class Main
{
    public static void main(String args[])throws IOException
    {
        Scanner obj=new Scanner(System.in);
        int i,c=0;String ns="";
        String s=obj.nextLine();
        String t=obj.nextLine();
        for(i=0;i<s.length();i++)
           {
               if(s.charAt(i)!=t.charAt(i))
                    c++;
               else
                    continue;
            }
        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