import java.util.*;
 
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String a = sc.next();
    String b = sc.next();
    int ans;
    ans = convert(a,b);
    System.out.println(ans);
  }
  public static int convert(String a, String b){
      int l = a.length();
      int count = 0;
      for(int i =0; i< l; i++){
          if(a.charAt(i) != b.charAt(i))
            count++;
      }
      return 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