import java.util.Scanner;

public class Main{

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner kb = new Scanner(System.in);
		String s = kb.next();
		String t = kb.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count += 1;
		}

		System.out.println(count);
		kb.close();
	}

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

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner kb = new Scanner(System.in);
		String s = kb.next();
		String t = kb.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count += 1;
		}

		System.out.println(count);
		kb.close();
	}

} Main public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner kb = new Scanner(System.in);
		String s = kb.next();
		String t = kb.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count += 1;
		}

		System.out.println(count);
		kb.close();
	} main {
		// TODO Auto-generated method stub
		Scanner kb = new Scanner(System.in);
		String s = kb.next();
		String t = kb.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count += 1;
		}

		System.out.println(count);
		kb.close();
	} Scanner kb = new Scanner(System.in); kb new Scanner(System.in) String s = kb.next(); s kb.next() kb.next kb String t = kb.next(); t kb.next() kb.next kb int count = 0; count 0 for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count += 1;
		} 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))
				count += 1;
		} {
			if (s.charAt(i) != t.charAt(i))
				count += 1;
		} if (s.charAt(i) != t.charAt(i))
				count += 1; s.charAt(i) != t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i count += 1 count 1 System.out.println(count) System.out.println System.out System System.out count kb.close() kb.close kb String[] args args public class Main{

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner kb = new Scanner(System.in);
		String s = kb.next();
		String t = kb.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count += 1;
		}

		System.out.println(count);
		kb.close();
	}

} public class Main{

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner kb = new Scanner(System.in);
		String s = kb.next();
		String t = kb.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count += 1;
		}

		System.out.println(count);
		kb.close();
	}

} Main
import java.util.Scanner;

public class Main{

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner kb = new Scanner(System.in);
		String s = kb.next();
		String t = kb.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count += 1;
		}

		System.out.println(count);
		kb.close();
	}

}
