import java.util.Scanner;

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

                String S = scan.next();
                String T = scan.next();

                int count = 0;

                for (int i = 0; i < S.length(); i++) {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                }

                System.out.println(count);

                scan.close();

        }

} import java.util.Scanner; Scanner java.util public class Main {
        public static void main(String[] args) {
                Scanner scan = new Scanner(System.in);

                String S = scan.next();
                String T = scan.next();

                int count = 0;

                for (int i = 0; i < S.length(); i++) {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                }

                System.out.println(count);

                scan.close();

        }

} Main public static void main(String[] args) {
                Scanner scan = new Scanner(System.in);

                String S = scan.next();
                String T = scan.next();

                int count = 0;

                for (int i = 0; i < S.length(); i++) {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                }

                System.out.println(count);

                scan.close();

        } main {
                Scanner scan = new Scanner(System.in);

                String S = scan.next();
                String T = scan.next();

                int count = 0;

                for (int i = 0; i < S.length(); i++) {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                }

                System.out.println(count);

                scan.close();

        } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String S = scan.next(); S scan.next() scan.next scan String T = scan.next(); T scan.next() scan.next scan int count = 0; count 0 for (int i = 0; i < S.length(); i++) {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                } int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                } {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                } if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	} !S.substring(i, i+1).equals(T.substring(i, i+1)) S.substring(i, i+1).equals(T.substring(i, i+1)) S.substring(i, i+1).equals S.substring(i, i+1) S.substring S i i+1 i 1 T.substring(i, i+1) T.substring T i i+1 i 1 {
                		count++;
                	} count++ count System.out.println(count) System.out.println System.out System System.out count scan.close() scan.close scan String[] args args public class Main {
        public static void main(String[] args) {
                Scanner scan = new Scanner(System.in);

                String S = scan.next();
                String T = scan.next();

                int count = 0;

                for (int i = 0; i < S.length(); i++) {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                }

                System.out.println(count);

                scan.close();

        }

} public class Main {
        public static void main(String[] args) {
                Scanner scan = new Scanner(System.in);

                String S = scan.next();
                String T = scan.next();

                int count = 0;

                for (int i = 0; i < S.length(); i++) {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                }

                System.out.println(count);

                scan.close();

        }

} Main
import java.util.Scanner;

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

                String S = scan.next();
                String T = scan.next();

                int count = 0;

                for (int i = 0; i < S.length(); i++) {
                	if (!S.substring(i, i+1).equals(T.substring(i, i+1))) {
                		count++;
                	}
                }

                System.out.println(count);

                scan.close();

        }

}