import java.util.*;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String word = sc.nextLine();
        String word1 = sc.nextLine();
        int counter = 0;
        for(int p=0; p<word.length(); p++){
            if(word.charAt(p) != word1.charAt(p)){
                ++counter;
            }

        }
        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