import java.util.*;

class Main{
  static public void main(String[] args){
    Scanner sc=new Scanner(System.in);
    String str1=sc.nextLine(),str2=sc.nextLine();
    int num=0;
    for(int i=0;i<str1.length();i++)
      if(str1.charAt(i)!=str2.charAt(i))
        num++;
   
    System.out.println(num);
  }
}
/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