import java.util.*;
public class Main {

    public static void main(String[] args)
    {
        Scanner in=new Scanner(System.in);
        String S = in.next();
        String T = in.next();
        int count = 0;
        if (S.length() == T.length()){
            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