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;
        }
    }
} import java.util.*; util.* java import java.io.*; io.* java 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;
        }
    }
} 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();
    } main {
        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();
    } InputReader in = new InputReader(System.in); in new InputReader(System.in) PrintWriter pw = new PrintWriter(new OutputStreamWriter(System.out)); pw new PrintWriter(new OutputStreamWriter(System.out)) String s1 = in.next(); s1 in.next() in.next in String s2 = in.next(); s2 in.next() in.next in int count = 0; count 0 for (int i = 0; i < s1.length(); i++) {
            if(s1.charAt(i) != s2.charAt(i)) {
                count++;
            }
        } int i = 0; int i = 0; i 0 i < s1.length() i s1.length() s1.length s1 i++ i++ i {
            if(s1.charAt(i) != s2.charAt(i)) {
                count++;
            }
        } {
            if(s1.charAt(i) != s2.charAt(i)) {
                count++;
            }
        } if(s1.charAt(i) != s2.charAt(i)) {
                count++;
            } s1.charAt(i) != s2.charAt(i) s1.charAt(i) s1.charAt s1 i s2.charAt(i) s2.charAt s2 i {
                count++;
            } count++ count pw.println(count) pw.println pw count pw.close() pw.close pw String[] args args /******************************
     ** IO STUFF STARTS FROM HERE**
     ******************************/

    static void debug(Object...obj) {
        System.err.println(Arrays.deepToString(obj));
    } debug {
        System.err.println(Arrays.deepToString(obj));
    } System.err.println(Arrays.deepToString(obj)) System.err.println System.err System System.err Arrays.deepToString(obj) Arrays.deepToString Arrays obj Object...obj 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;
        }
    } InputReader public BufferedReader reader; reader public StringTokenizer tokenizer; tokenizer public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream));
            tokenizer = null;
        } InputReader {
            reader = new BufferedReader(new InputStreamReader(stream));
            tokenizer = null;
        } reader = new BufferedReader(new InputStreamReader(stream)) reader new BufferedReader(new InputStreamReader(stream)) tokenizer = null tokenizer null InputStream stream stream //InputReader in = new InputReader(new FileReader("File_Name"));
        public InputReader(FileReader file) {
            reader = new BufferedReader(file);
            tokenizer = null;
        } InputReader {
            reader = new BufferedReader(file);
            tokenizer = null;
        } reader = new BufferedReader(file) reader new BufferedReader(file) tokenizer = null tokenizer null FileReader file file public String next() {

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

            return tokenizer.nextToken();
        } next {

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

            return tokenizer.nextToken();
        } try {
                while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                return null;
            } catch (IOException e) {
                return null;
            } IOException e {
                return null;
            } return null; null {
                while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine());
            } while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine()); tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public String nextLine() {
            String line = null;
            try {
                tokenizer = null;
                line =  reader.readLine();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
            return line;
        } nextLine {
            String line = null;
            try {
                tokenizer = null;
                line =  reader.readLine();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
            return line;
        } String line = null; line null try {
                tokenizer = null;
                line =  reader.readLine();
            } catch (IOException e) {
                throw new RuntimeException(e);
            } catch (IOException e) {
                throw new RuntimeException(e);
            } IOException e {
                throw new RuntimeException(e);
            } throw new RuntimeException(e); new RuntimeException(e) {
                tokenizer = null;
                line =  reader.readLine();
            } tokenizer = null tokenizer null line =  reader.readLine() line reader.readLine() reader.readLine reader return line; line public int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public double nextDouble() {
            return Double.parseDouble(next());
        } nextDouble {
            return Double.parseDouble(next());
        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public boolean hasNext(){
            try {
                while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine());
            }
            catch (Exception e) {
                return false;
            }
            return true;
        } hasNext {
            try {
                while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine());
            }
            catch (Exception e) {
                return false;
            }
            return true;
        } try {
                while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine());
            }
            catch (Exception e) {
                return false;
            } catch (Exception e) {
                return false;
            } Exception e {
                return false;
            } return false; false {
                while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine());
            } while (tokenizer == null || !tokenizer.hasMoreTokens())
                    tokenizer = new StringTokenizer(reader.readLine()); tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return true; true 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;
        }
    }
} 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;
        }
    }
} Main
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;
        }
    }
}