import java.util.Scanner;

public class Main {

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

		 String a = s.next();
		 String b = s.next();

		 String[] strArrayA = a.split("");
		 String[] strArrayB = b.split("");

		 int cnt = 0;

		 for(int i=0; i<a.length(); i++) {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 }

		 System.out.println(cnt);
	}

} import java.util.Scanner; Scanner java.util public class Main {

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

		 String a = s.next();
		 String b = s.next();

		 String[] strArrayA = a.split("");
		 String[] strArrayB = b.split("");

		 int cnt = 0;

		 for(int i=0; i<a.length(); i++) {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 }

		 System.out.println(cnt);
	}

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

		 String a = s.next();
		 String b = s.next();

		 String[] strArrayA = a.split("");
		 String[] strArrayB = b.split("");

		 int cnt = 0;

		 for(int i=0; i<a.length(); i++) {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 }

		 System.out.println(cnt);
	} main {
		 Scanner s = new Scanner(System.in);

		 String a = s.next();
		 String b = s.next();

		 String[] strArrayA = a.split("");
		 String[] strArrayB = b.split("");

		 int cnt = 0;

		 for(int i=0; i<a.length(); i++) {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 }

		 System.out.println(cnt);
	} Scanner s = new Scanner(System.in); s new Scanner(System.in) String a = s.next(); a s.next() s.next s String b = s.next(); b s.next() s.next s String[] strArrayA = a.split(""); strArrayA a.split("") a.split a "" String[] strArrayB = b.split(""); strArrayB b.split("") b.split b "" int cnt = 0; cnt 0 for(int i=0; i<a.length(); i++) {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 } int i=0; int i=0; i 0 i<a.length() i a.length() a.length a i++ i++ i {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 } {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 } String strA = String.valueOf(a.charAt(i)); strA String.valueOf(a.charAt(i)) String.valueOf String a.charAt(i) a.charAt a i String strB = String.valueOf(b.charAt(i)); strB String.valueOf(b.charAt(i)) String.valueOf String b.charAt(i) b.charAt b i if(strA.equals(strB) == false) {
				 cnt++;
			 } strA.equals(strB) == false strA.equals(strB) strA.equals strA strB false {
				 cnt++;
			 } cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main {

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

		 String a = s.next();
		 String b = s.next();

		 String[] strArrayA = a.split("");
		 String[] strArrayB = b.split("");

		 int cnt = 0;

		 for(int i=0; i<a.length(); i++) {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 }

		 System.out.println(cnt);
	}

} public class Main {

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

		 String a = s.next();
		 String b = s.next();

		 String[] strArrayA = a.split("");
		 String[] strArrayB = b.split("");

		 int cnt = 0;

		 for(int i=0; i<a.length(); i++) {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 }

		 System.out.println(cnt);
	}

} Main
import java.util.Scanner;

public class Main {

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

		 String a = s.next();
		 String b = s.next();

		 String[] strArrayA = a.split("");
		 String[] strArrayB = b.split("");

		 int cnt = 0;

		 for(int i=0; i<a.length(); i++) {
			 String strA = String.valueOf(a.charAt(i));
			 String strB = String.valueOf(b.charAt(i));
			 if(strA.equals(strB) == false) {
				 cnt++;
			 }
		 }

		 System.out.println(cnt);
	}

}