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