import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.next();
        String t = scanner.next();
        int count = 0;
        char[] ss = s.toCharArray();
        char[] tt = t.toCharArray();

        for (int i = 0; i < s.length(); i++) {
            if (ss[i] != tt[i]) {
                count = 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