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.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		}
		System.out.println(count);

	}

} 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.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		}
		System.out.println(count);

	}

} 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.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		}
		System.out.println(count);

	} 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.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		}
		System.out.println(count);

	} 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.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		} int i=0; int i=0; i 0 i<s.length() i s.length() s.length s i++ i++ i {
			if(s.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		} {
			if(s.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		} if(s.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			} s.charAt(i) == t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i {
				continue;
			} continue; {
				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 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.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		}
		System.out.println(count);

	}

} 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.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		}
		System.out.println(count);

	}

} 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.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				count++;
			}
		}
		System.out.println(count);

	}

}
