import java.util.Scanner;

public class Main {
	public static void main(String args[]) {

		Scanner n = new Scanner(System.in);

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

		String[] S_list = S.split("");
		String[] T_list = T.split("");


		int count = 0;
		for(int i=0;i<S.length();i++) {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		}
		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String args[]) {

		Scanner n = new Scanner(System.in);

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

		String[] S_list = S.split("");
		String[] T_list = T.split("");


		int count = 0;
		for(int i=0;i<S.length();i++) {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		}
		System.out.println(count);
	}
} Main public static void main(String args[]) {

		Scanner n = new Scanner(System.in);

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

		String[] S_list = S.split("");
		String[] T_list = T.split("");


		int count = 0;
		for(int i=0;i<S.length();i++) {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		}
		System.out.println(count);
	} main {

		Scanner n = new Scanner(System.in);

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

		String[] S_list = S.split("");
		String[] T_list = T.split("");


		int count = 0;
		for(int i=0;i<S.length();i++) {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		}
		System.out.println(count);
	} Scanner n = new Scanner(System.in); n new Scanner(System.in) String S = n.next(); S n.next() n.next n String T = n.next(); T n.next() n.next n String[] S_list = S.split(""); S_list S.split("") S.split S "" String[] T_list = T.split(""); T_list T.split("") T.split T "" int count = 0; count 0 for(int i=0;i<S.length();i++) {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		} int i=0; int i=0; i 0 i<S.length() i S.length() S.length S i++ i++ i {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		} {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		} if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			} S_list[i].equals(T_list[i]) S_list[i].equals S_list[i] S_list i T_list[i] T_list i {

			} {
				count++;
			} count++ count System.out.println(count) System.out.println System.out System System.out count String args[] args public class Main {
	public static void main(String args[]) {

		Scanner n = new Scanner(System.in);

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

		String[] S_list = S.split("");
		String[] T_list = T.split("");


		int count = 0;
		for(int i=0;i<S.length();i++) {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		}
		System.out.println(count);
	}
} public class Main {
	public static void main(String args[]) {

		Scanner n = new Scanner(System.in);

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

		String[] S_list = S.split("");
		String[] T_list = T.split("");


		int count = 0;
		for(int i=0;i<S.length();i++) {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		}
		System.out.println(count);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String args[]) {

		Scanner n = new Scanner(System.in);

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

		String[] S_list = S.split("");
		String[] T_list = T.split("");


		int count = 0;
		for(int i=0;i<S.length();i++) {
			if(S_list[i].equals(T_list[i])) {

			}else {
				count++;
			}
		}
		System.out.println(count);
	}
}
