import java.util.*;
public class Main {
    public static void main(String[] args){

		Scanner sc = new Scanner(System.in);

		String S = sc.next();		
      String T = sc.next();
      int swap = 0;
      
      int length = S.length();
      for(int i=0;i<length;i++){
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      }
	  System.out.println(swap);
		
		
    }
}
/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