import java.util.*;
import java.io.*;

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