
import java.util.Scanner;

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

		int ans = 0;
		for (int i = 0; i < s.length(); i++) {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		}
		System.out.println(ans);

	}

} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();

		int ans = 0;
		for (int i = 0; i < s.length(); i++) {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		}
		System.out.println(ans);

	}

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

		int ans = 0;
		for (int i = 0; i < s.length(); i++) {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		}
		System.out.println(ans);

	} main {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();

		int ans = 0;
		for (int i = 0; i < s.length(); i++) {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		}
		System.out.println(ans);

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc String t = sc.next(); t sc.next() sc.next sc int ans = 0; ans 0 for (int i = 0; i < s.length(); i++) {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		} int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		} {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		} if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++; !s.substring(i, i + 1).equals(t.substring(i, i + 1)) s.substring(i, i + 1).equals(t.substring(i, i + 1)) s.substring(i, i + 1).equals s.substring(i, i + 1) s.substring s i i + 1 i 1 t.substring(i, i + 1) t.substring t i i + 1 i 1 ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();

		int ans = 0;
		for (int i = 0; i < s.length(); i++) {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		}
		System.out.println(ans);

	}

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

		int ans = 0;
		for (int i = 0; i < s.length(); i++) {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		}
		System.out.println(ans);

	}

} Main

import java.util.Scanner;

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

		int ans = 0;
		for (int i = 0; i < s.length(); i++) {
			if (!s.substring(i, i + 1).equals(t.substring(i, i + 1)))
				ans++;
		}
		System.out.println(ans);

	}

}
