import java.util.Scanner;
public class Main{
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String s = input.next();
        String t = input.next();
        int counter = 0;
        int j = 0;
        for(int i = 0; i < s.length();i++){
                if(s.charAt(i) != t.charAt(j))
                    counter++;
            j++;
        }
        System.out.println(counter);
    }
}

/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