
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();
		sc.close();
		int c=0;
		for (int i = 0; i < s.length(); i++) {
			if(s.charAt(i) == t.charAt(i)) continue;
			c++;
		}
		System.out.println(c);

	}

} 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();
		sc.close();
		int c=0;
		for (int i = 0; i < s.length(); i++) {
			if(s.charAt(i) == t.charAt(i)) continue;
			c++;
		}
		System.out.println(c);

	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		sc.close();
		int c=0;
		for (int i = 0; i < s.length(); i++) {
			if(s.charAt(i) == t.charAt(i)) continue;
			c++;
		}
		System.out.println(c);

	} main {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		sc.close();
		int c=0;
		for (int i = 0; i < s.length(); i++) {
			if(s.charAt(i) == t.charAt(i)) continue;
			c++;
		}
		System.out.println(c);

	} 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 sc.close() sc.close sc int c=0; c 0 for (int i = 0; i < s.length(); i++) {
			if(s.charAt(i) == t.charAt(i)) continue;
			c++;
		} 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;
			c++;
		} {
			if(s.charAt(i) == t.charAt(i)) continue;
			c++;
		} if(s.charAt(i) == t.charAt(i)) continue; s.charAt(i) == t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i continue; c++ c System.out.println(c) System.out.println System.out System System.out c 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();
		sc.close();
		int c=0;
		for (int i = 0; i < s.length(); i++) {
			if(s.charAt(i) == t.charAt(i)) continue;
			c++;
		}
		System.out.println(c);

	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		sc.close();
		int c=0;
		for (int i = 0; i < s.length(); i++) {
			if(s.charAt(i) == t.charAt(i)) continue;
			c++;
		}
		System.out.println(c);

	}

} 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();
		sc.close();
		int c=0;
		for (int i = 0; i < s.length(); i++) {
			if(s.charAt(i) == t.charAt(i)) continue;
			c++;
		}
		System.out.println(c);

	}

}
