import java.util.Scanner;

public class Main {
        public static void main(String[] args) {
                Scanner scan = new Scanner(System.in);

                String S = scan.next();
                String T = scan.next();

                int count = 0;

                for (int i = 0; i < S.length(); i++) {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                }

                System.out.println(count);

                scan.close();

        }

}
/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