import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
		 String N = sc.next();
		 String S = sc.next();
		 int count =0;
		 for (int i = 0; i < N.length(); i++) {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 }
		 System.out.print(count);
	}
}
 import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
		 String N = sc.next();
		 String S = sc.next();
		 int count =0;
		 for (int i = 0; i < N.length(); i++) {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 }
		 System.out.print(count);
	}
} Main public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
		 String N = sc.next();
		 String S = sc.next();
		 int count =0;
		 for (int i = 0; i < N.length(); i++) {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 }
		 System.out.print(count);
	} main {
		 Scanner sc = new Scanner(System.in);
		 String N = sc.next();
		 String S = sc.next();
		 int count =0;
		 for (int i = 0; i < N.length(); i++) {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 }
		 System.out.print(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String N = sc.next(); N sc.next() sc.next sc String S = sc.next(); S sc.next() sc.next sc int count =0; count 0 for (int i = 0; i < N.length(); i++) {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 } int i = 0; int i = 0; i 0 i < N.length() i N.length() N.length N i++ i++ i {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 } {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 } if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 } N.charAt(i) == S.charAt(i) N.charAt(i) N.charAt N i S.charAt(i) S.charAt S i { 
			 } {
				 count++;
			 } count++ count System.out.print(count) System.out.print System.out System System.out count String[] args args public class Main {

	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
		 String N = sc.next();
		 String S = sc.next();
		 int count =0;
		 for (int i = 0; i < N.length(); i++) {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 }
		 System.out.print(count);
	}
} public class Main {

	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
		 String N = sc.next();
		 String S = sc.next();
		 int count =0;
		 for (int i = 0; i < N.length(); i++) {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 }
		 System.out.print(count);
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
		 String N = sc.next();
		 String S = sc.next();
		 int count =0;
		 for (int i = 0; i < N.length(); i++) {
			 if (N.charAt(i) == S.charAt(i)) { 
			 } else {
				 count++;
			 }
		 }
		 System.out.print(count);
	}
}

