import java.util.*;
public class Main{
  public static void main(String[] args){
    Scanner sc =new Scanner(System.in);
    String S =sc.next();
    String s[] =S.split("",0);
    String T =sc.next();
    String t[] =T.split("",0);
    int N =S.length();
    int a=N;
    for(int i=0;i<N;i++){
      if(s[i].equals(t[i])){a=a-1;}}
    System.out.println(a);
  }
}

/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