import java.util.*;
public class Main {

    public static void main(String[] args) throws Exception {
        Scanner sc = null;
        sc = new Scanner(System.in);
        String s = sc.nextLine();	
        String t = sc.nextLine();
        sc.close();	
        char[] cs = s.toCharArray();
        char[] ct = t.toCharArray();
        int count = 0;
        for (int i = 0; i < cs.length; i++) {
            if (cs[i] != ct[i]) {
                count +=1;
            } 
        }
        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