import java.util.Scanner;

public class Main {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        String text1 = sc.nextLine();
        String text2 = sc.nextLine();

        int wordNum = text1.length();
        int diffCount=0;

        for(int i=0;i<wordNum;i++){
            if(text1.charAt(i) != text2.charAt(i)){
                diffCount +=1;
            }
        }
        System.out.println(diffCount);
    }
}
/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