import java.util.*;
import java.io.*;

public class Main {

    public static void main(String[] args)throws Exception {
        InputReader in = new InputReader(System.in);
        PrintWriter pw = new PrintWriter(new OutputStreamWriter(System.out));
        // write your code here //
        String s1 = in.next();
        String s2 = in.next();
        int count = 0;
        for (int i = 0; i < s1.length(); i++) {
            if(s1.charAt(i) != s2.charAt(i)) {
                count++;
            }
        }
        pw.println(count);

        pw.close();
    }



    /******************************
     ** IO STUFF STARTS FROM HERE**
     ******************************/

    static void debug(Object...obj) {
        System.err.println(Arrays.deepToString(obj));
    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream));
            tokenizer = null;
        }

        //InputReader in = new InputReader(new FileReader("File_Name"));
        public InputReader(FileReader file) {
            reader = new BufferedReader(file);
            tokenizer = null;
        }

        public String next() {

            try {
                while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                return null;
            }

            return tokenizer.nextToken();
        }

        public String nextLine() {
            String line = null;
            try {
                tokenizer = null;
                line =  reader.readLine();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
            return line;
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public boolean hasNext(){
            try {
                while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine());
            }
            catch (Exception e) {
                return false;
            }
            return true;
        }
    }
}
/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