import java.util.Scanner;
 
public class Main {
  public static void main(String[] args ) {
    Scanner sc = new Scanner(System.in);
    
    String a = sc.next();
    String b = sc.next();
    
    char[] A = new char[a.length()];
    for(int i =0; i< a.length(); i++){
      A[i]=a.charAt(i);
    }
    char[] B = new char[a.length()];
    for(int i =0; i< a.length(); i++){
      B[i]=b.charAt(i);
    }
    
    int num=0;
    for (int i =0; i< a.length(); i++){
      if (A[i]!=B[i]) {
        num = num + 1;
      }
    }
    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