import java.util.*;
    public class Main{
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            String s = sc.nextLine();
            String t = sc.nextLine();
            int count=0;
            for (int i=1;i <= s.length(); i++) {
                if(!s.substring(i-1,i).equals(t.substring(i-1,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